land snail

Late Miocene–Pliocene Paleoclimatic Evolution Documented by Terrestrial Mollusk Populations in the Western Chinese Loess Plateau

Fengjiang Li1*,Naiqin Wu1,Denis-Didier Rousseau2,3,Yajie Dong1,Dan Zhang1,Yunpeng Pei4

1Key Laboratory of Cenozoic Geology and Environment,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing,China,2Laboratoire de Meteorologie Dynamique,UMR INSU-CNRS8539&CERES-ERTI,Ecole Normale Superieure,Paris,France,3Lamont-Doherty Earth Observatory of Columbia University,Palisades,New York,United States of America,4School of the Earth Sciences and Resources,China University of Geosciences,Beijing,China

Abstract

The Neogene eolian deposits in the Chinese Loess Plateau(CLP)are one of the most useful continental deposits for understanding climatic changes.To decipher Late Neogene paleoclimatic changes in the CLP,we present a terrestrial mollusk record spanning the time interval between7.1and3.5Ma from the western CLP.The results indicate four stages of paleoclimatic evolution:From7.1to6.2Ma,cold and dry climatic conditions prevailed as evidenced by high values of the total number of cold-aridiphilous(CA)mollusk species and by low values of all of the thermo-humidiphilous(TH)mollusk indices.From6.2to5.4Ma,the climate remained cold and dry but was not quite as dry as during the preceding phase,as indicated by the dominance of CA mollusks and more TH species and individuals.From5.4to4.4Ma,a warm and moist climate prevailed,as indicated by high values of the TH species and individuals and by the sparsity of CA species and individuals.From4.4to3.5Ma,all of the CA indices increased significantly and maintained high values;all of the TH indices exhibit high values from4.4to4.0Ma,an abrupt decrease from4.0Ma and a further increase from3.7Ma.The CA species of Cathaica pulveraticula,Cathaica schensiensis,and Pupopsis retrodens are only identified in this stage,indicating that the CA species were diversified and that the climate was becoming drier.Moreover,the CA mollusk group exhibits considerable diversity from7.1to5.4Ma when a cold,dry climate prevailed;whereas the diversity of the TH group was high during the relatively warm,wet interval from5.4to4.4Ma.This indicates that variations in the diversity of the CA and TH mollusk groups were closely related to climatic changes during the Late Miocene to Pliocene.

Citation:Li F,Wu N,Rousseau D-D,Dong Y,Zhang D,et al.(2014)Late Miocene–Pliocene Paleoclimatic Evolution Documented by Terrestrial Mollusk Populations in the Western Chinese Loess Plateau.PLoS ONE9(4):e95754.doi:10.1371/journal.pone.0095754

Editor:Lorenzo Rook,University of Florence,Italy

Received December27,2013;Accepted March29,2014;Published April21,2014

Copyright:?2014Li et al.This is an open-access article distributed under the terms of the Creative Commons Attribution License,which permits unrestricted use,distribution,and reproduction in any medium,provided the original author and source are credited.

Funding:This study is supported by the Chinese Academy of Sciences(KZCX2-EW-QN107),the National Basic Research Program of China(No.2010CB950204), the Strategic Priority Research Program:Climate Change,Carbon Budget and Relevant Issues(XDA05120203),the National Natural Science Foundation of China (Projects41072130,41272205,and41230104),and part of the work was achieved during a stay in Paris through a CNRS-NSFC grant.This is Lamont-Doherty Earth Observatory contribution7763.The funders had no role in study design,data collection and analysis,decision to publish,or preparation of the manuscript.

Competing Interests:The authors have declared that no competing interests exist.

*E-mail:fengjiangli@https://www.doczj.com/doc/3111539753.html,

Introduction

As evidenced by the marine benthic foraminiferal d18O record, Earth’s climate underwent a gradual cooling trend during the Late Miocene and Pliocene.This interval witnessed the progressive cooling of oceanic deep water,the expansion of permanent ice sheets in Antarctica,the occurrence of ice rafted detritus in Northern Hemisphere(mostly in north Atlantic),and both hemispheres covered by ice sheets after middle Pliocene[1]. Coincident with ice development in both Polar regions are significant ecological,climatic,and tectonic events elsewhere and especially around Asia[1–12],and which demonstrate that the Late Miocene and Pliocene was an important and complex interval that needs to be better understood.

In East Asia,one of the most important climatic changes is the evolution of the East Asian(EA)monsoon.Numerous sedimen-tological,geochemical,and paleontological studies,including of fossil mammals,mainly from the Chinese Loess Plateau(CLP)and the South China Sea(SCS),have contributed significantly to our understanding of the EA monsoon changes during the Late Miocene to Pliocene.However,the results are inconsistent and some are even in conflict.In the CLP,sedimentological evidence of changes in sediment grain size and sedimentation rate from the Xifeng,Lingtai,Lantian,Xunyi,Luochuan,Jiaxian,Baode,and Jingle(Figure1)Red Clay deposits indicate the occurrence of a strong winter monsoon and pronounced aridity in the Asian interior during the Late Miocene[8,13–16].However,the geochemical record of87Sr/86Sr ratios from the Lingtai Red Clay sequence implies a weak EA winter monsoon from7to2.5Ma [17];and in addition,this interval can be sub-divided into a large amplitude and high frequency stage from7–4.2Ma and a weak, stable stage from4.2–2.6Ma,as evidenced by records of Zr/Rb ratio and mean quartz grain size[18].Furthermore,grain-size records from fluvial deposits in the Linxia Basin(Figure1)indicate that the EA winter monsoon intensified at7.4Ma and5.3Ma [19],the latter datum being significantly different to evidence from the Red Clay record.

In the case of the EA summer monsoon,the magnetic susceptibility record from the Xifeng Red Clay sequence indicates a weakened summer monsoon during the Late Miocene(6–5.4

Ma)and a strong summer monsoon during the early Pliocene [8].Additional information about the EA summer monsoon is provided by records of pedostratigraphy and iron geochemistry from the Lingtai Red Clay deposits.These records indicate that the EA summer monsoon was relatively weak from 7.05to 6.2Ma,strengthened from 6.2to 5.5Ma,was very strong from 5.5to 3.85Ma corresponding to the interval of strongest soil development,and weakened significantly over the interval 3.85to 3.15Ma [20,21].

However,studies of mammalian fossils from the CLP have yielded very different results:Hypsodonty analysis indicates that northern China became more humid at 7–8Ma,coincident with the onset of Red Clay deposition in the eastern CLP,and which was interpreted by the authors as representing the onset or intensification of summer monsoonal precipitation [22,23].A general rise in d 18O values of soil carbonate from the Lantian fluvial and Red Clay deposits reflects increased summer precip-itation related to the onset and/or intensification of the EA monsoon during the Late Miocene to Pliocene [24,25],and which is supported by a mammalian faunal turnover event implying a marked change to more humid and closed habitats [26].Recent isotopic evidence from fossil mammals and soil carbonates indicates a strengthened EA summer monsoon from 7–4Ma [27].However,the d 13C values of fossil enamel from a diverse group of herbivores and of paleosol carbonate and organic matter

from the Linxia Basin indicate that C4grasses were either absent or insignificant in the Linxia Basin prior to 2–3Ma,suggesting that the EA summer monsoon was probably not strong enough to affect this part of China throughout much of the Neogene [28].However,this result conflicts with the interpretations of Fortelius et al.(2002)[22],Kaakinen et al.(2006,2013)[24,25],Liu et al.(2009)[23]and Passey et al.(2009)[27].

In the SCS,the EA winter monsoon developed progressively from 7Ma as shown by an increasing trend in black carbon concentration and accumulation rate [29].In addition the EA summer monsoon weakened after 7.5Ma,as evidenced by combined planktonic foraminiferal Mg/Ca and d 18O records [30],consistent with the Red Clay sequences in the CLP.The suggestion of a weakened EA summer monsoon is supported by geochemical records which indicate that chemical weathering intensity decreased from the early Miocene with a rapid decrease centered at 7.2Ma [31].This result is generally consistent with records of radiolarian species numbers and individuals,and diversity,from the southern SCS and which suggest a major decrease in summer monsoon intensity after 7.70Ma [32].In contrast,records of clay/feldspar ratio,kaolinite/chlorite ratio and biogenic opal MAR from the SCS suggest that the summer monsoon was strong from 7.1–6.2Ma and remained relatively stable from 6.2–3.5Ma [33];however,the authors emphasize

that

Figure 1.Location of the Chinese Loess Plateau (CLP),the studied Dongwan loess-paleosol sequence and other Neogene sections mentioned in the text.The Dongwan sequence is indicated by a red circle and other sections by white circles.Main cities are indicated by black squares.

doi:10.1371/journal.pone.0095754.g001

their study is a schematic reconstruction which only outlines the principal stages but neglects the details.

A semi-quantitative reconstruction of the Neogene vegetation in China indicates that Miocene aridification associated with strengthening of the EA winter monsoon is consistent with Neogene global cooling,and that the EA summer monsoon did not weaken during the Pliocene[34],and this result agrees with most of the geological records from the CLP and SCS.However another quantitative reconstruction from plant fossil records yielded contrasting results,indicating that records of both temperature and precipitation from north China exhibit no significant difference between the western and eastern regions during the Miocene,suggesting that the monsoon climate did not commence or intensify at that time[35].Regional climate model experiments also reveal that during the Late Miocene,from11–7 Ma,the monsoonal climate may not have been fully established in various Asian regions,including northern China[36];and this finding is contrary to that of numerous previous studies of the EA monsoon which suggest that it was initiated around the time of the Oligocene/Miocene boundary[37–39].

The foregoing review demonstrates that more work is needed to better understand the evolution of the EA monsoon during the Late Miocene and Pliocene.In particular,higher resolution studies using more sensitive monsoon proxies from key monsoon-dominated regions may be one of the best solutions for resolving the various inconsistencies and even conflicts regarding the process of monsoon development.

As mentioned above,the CLP(Figure1),located to the northeast of the Tibetan Plateau,is a key continental region for the study of the EA monsoon.Deposition of eolian sediments commenced in the western CLP from22Ma,as observed in the QA-I,QA-II,and QA-III(Figure1)Miocene loess-paleosol sequences which have a basal age of about22Ma[37,40],while the upper boundary is dated at about3.5Ma in the Dongwan late Miocene-Pliocene loess-paleosol sequence in the western CLP [41].In contrast,in the eastern CLP,the age of the lower boundary of eolian deposits,the Red Clay sequences,is about7–8 Ma as evidenced in the Lingtai,Xifeng,Liantian,and Baode sequences[15,20,42,43].However,results from the recently reported Shilou Red Clay sequence indicate that eolian sediments were deposited from11Ma in the eastern CLP[44].Despite the occurrence of a totally different lower boundary age between the east and west CLP,these deposits have great potential for deciphering in detail the processes of ecological and climatic evolution in the CLP,and by extension in East Asia,during the Miocene and Pliocene.As reviewed above,sedimentological and geochemical studies have so far contributed a great deal to our understanding of climatic changes during the interval of interest [6,8,9,13–18,20,21,24,27,37,40–45];however,to date there has been only a limited application of a biological approach to analyzing these sequences[22,26,46,47].

Land snails are generally the most common and abundant fossils in Quaternary loess sequences,and this fact,together with the limited degree of success of most of the other paleontological studies of Quaternary loess,makes them especially important paleoenvionmental indicators for loess deposits.Their occurrence in Quaternary loess was first documented in Europe in the early 1820s[48],and since then they have contributed significantly to understanding the origin and paleoclimatic evolution of Quater-nary loess deposits in Eurasia and especially in the CLP[46,49–57].However,terrestrial mollusks preserved in the Neogene sequences in the CLP have not been investigated in detail until recently.Although they have provided crucial paleontological evidence for the wind-blown origin of the Neogene loess sequences in the western CLP[58,59],the ecological and climatic information that terrestrial mollusks may provide has not been well deciphered,with the exception of the record from the Xifeng Red Clay sequence spanning the interval from6.2to2.4Ma in the eastern CLP[46].Furthermore,it is unknown how terrestrial mollusk diversity varied in the CLP against the background of climate changes during the Neogene,since the necessary studies have not been performed.In this study,we studied the record of terrestrial mollusks preserved in the Late Miocene to Pliocene Dongwan section in order to investigate the evolution of paleoclimate and terrestrial mollusk diversity in the western CLP during the Late Miocene to Pliocene.

Materials and Methods

The Dongwan loess-paleosol sequence(105u479E,34u589N) [41]is located in the northeastern part of Qin’an County in the western CLP(Figure1).The current climate in Qin’an County is mainly controlled by the EA monsoon,with mean annual precipitation of about400–500mm and mean annual tempera-ture of,10.4u C.Mean July and January temperatures are ,22.7u C and23.4u C,respectively.Vegetation in the region corresponds to a semi-arid temperate steppe[60].

The Dongwan sequence,located in the western CLP,is the first counterpart of the Red Clay sequences in the eastern CLP[41]. The section is about73.7m thick,and is composed of84 distinguishable loess-paleosol couplets.The chronology of the sequence has been established by Hao and Guo(2004)[41]using magnetostratigraphic and micromammalian studies(Figure2). First,Hao and Guo(2004)[41]ascribed the approximate age of the sequence to the Late Miocene to Pliocene using micromam-malian fossil teeth sampled from20depths of the Dongwan sequence.Second,they defined a series of magnetozones based on 319oriented samples collected at20or25cm intervals and correlated them with the Geomagnetic Polarity Timescale[61]. Finally,they established a chronology using paleomagnetic reversals as age controls and interpolated in between them using the magnetic susceptibility age model developed by Kukla et al. (1990)[62].Their results yield an age duration of7.1to3.5Ma for the Dongwan loess-palaeosol sequence[41].

A total of310mollusk assemblages were collected from the Dongwan sequence using continuous20-cm-thick samples;howev-er,some intervals were sampled at intervals of10–50cm,according to lithological changes[58].About30kg of sediment were obtained for each sample.In the field,we progressively broke each sediment sample into smaller pieces of about0.5mm in diameter,at the same time collecting all available shells and visible broken pieces.No necessary permits for the described field investigations were needed. In the laboratory,we attempted to restore any broken shells,and then identified and counted them under a binocular microscope.All of the identifiable mollusk remains were considered in the individual totals using the method of Puisse′gur(1976)[63].All of the mollusk shells are stored in the Institute of Geology and Geophysics,Chinese Academy of Sciences.

For each mollusk assemblage,the numbers of species(S)and individuals were counted and a diversity index was calculated for all species,thermo-humidiphilous(TH)species,and cold-aridiphi-lous(CA)species in order to investigate changes in terrestrial mollusk populations and in different ecological groups.We used the most widely applied Shannon index[64],sometimes referred to as the‘Shannon–Weaver’index and sometimes as the ‘Shannon–Wiener’index by researchers,in order to calculate the values of diversity,H(S),of the total,TH,and CA species,as follows:

H ~{

X S i ~1

ni N

log 2

ni

N

where n i is the density measure (in this case the mollusk individuals)of the i -th species (I varying between 1and n );S is the number of species in the sample,and

N ~{

X S i ~1

n i

The theoretical maximum (H max )of diversity in any sample is

expressed as

H max ~log 2S

Equitability (or evenness,E)is expressed as

E ~

H H max

These indices have been applied to European and North American Quaternary terrestrial mollusk assemblages [65–67].

Results

Mollusk fossils are relatively abundant in the Dongwan sequence with significant concentrations at ,2m,10m,30m,50m,and 70m depth.Amongst the total of 310samples,298yielded 16439mollusk individuals and 12samples were barren.The maximum count reached 1121/30kg at 54m depth (Figure 3).Variations in total mollusk individuals parallel fluctuations in magnetic susceptibility [58],indicating that pedogenic processes such as carbonate dissolution did not affect the preserved assemblages [58].

A total of 24mollusk species were identified in the Dongwan section.They are all terrestrial taxa and consist of Gastrocopta armigerella (Reinhardt,1877),Gastrocopta sp.,Punctum orphana (Heude,1882),Punctum sp.,Metodontia huaiensis (Crosse,1882),Metodontia yantaiensis (Crosse et Debeaux,1863),Metodontia beresowskii (Moellendorff,1899),Metodontia cf.huaiensis ,Metodontia cf.yantaiensis ,Metodontia cf.beresowskii ,Metodontia sp.,Kaliella sp.,Macrochlamys sp.,Opeas sp.,Cathaica sp.,Cathaica pulveratrix (Martens,1882),Cathaica pulveraticula (Martens,1882),Cathaica schensiensis (Hilber,1883),Cathaica placenta (Ping et Yen,1933),Pupilla aeoli (Hilber,1883),Pupilla grabaui (Ping,1929),Pupilla sp.,Vallonia sp.,and Pupopsis retrodens (Martens,1879).

All of these species,except Pupilla grabaui and Pupopsis retrodens,have been previously identified in the Chinese Quaternary loess-paleosol sequences and most of them have modern representatives.For example,Cathaica pulveratrix ,C.pulveraticula ,C.schensiensis ,and Pupilla aeoli are the most common species that prefer living in relatively cold,dry environments,and are presently distributed in northwestern China.They have been regarded as indicative of

a

Figure 2.Chronology of the Dongwan loess-paleosol sequence (modified after Hao and Guo,2004)[41].doi:10.1371/journal.pone.0095754.g002

strengthened winter monsoon [49–58].Conversely,Metodontia huaiensis,M.yantaiensis ,M.beresowskii,Gastrocopta armigerella,and Punctum orphana are species living in a warmer and more humid environment,and are distributed mainly in the southeastern part of the CLP,where the warm,moist summer monsoon brings sufficient precipitation [49–58].Therefore based on their present requirements of moisture and temperature,as well as their modern geographical distribution,the Dongwan terrestrial mollusks can be grouped into CA and TH ecological groups,as have been previously defined in the Chinese Quaternary loess-paleosol sequences [49–57].In the Dongwan section,the TH group comprises Gastrocopta armigerella ,Gastrocopta sp.,Punctum orphana ,Punctum sp.,Metodontia beresowskii ,Metodontia huaiensis ,Metodontia yantaiensis ,Metodontia cf.huaiensis ,Metodontia cf.yantaiensis ,Metodontia cf.beresowskii ,Metodontia sp.,Kaliella sp.,Macrochlamys sp.,and Opeas sp.;and the CA group comprises Cathaica sp.,Cathaica pulveratrix ,Cathaica pulveraticula ,Cathaica schensiensis ,Cathaica placenta ,Pupilla aeoli ,Pupilla grabaui ,Pupilla sp.,Vallonia cf.pulchella ,Vallonia sp.,and Pupopsis retrodens .

The distributions of these terrestrial mollusks in the Dongwan section have been described previously [58].Cathaica sp.is the most continuously distributed mollusk taxon in the Dongwan section,and Gastrocopta sp.,Pupilla sp.,and Vallonia sp.are other well represented taxa.The TH species of Metodontia ,Punctum ,Macrochlamys ,and Opeas are concentrated in the upper part of the section.In general,the CA species are dominant in the loess layers,while the TH species mainly occur in the paleosols [58].

Variations in the number of species (S),diversity (H ),equitability (E),and total individuals of all species,CA species,and TH species in the Dongwan sequence are plotted against depth in Figure 3.These data can be found in the supporting information data (Table S1).Variations in these parameters allow definition of four mollusk zones.In Zone 1,from the bottom of the sequence to

about 56.8m depth (,7.1–6.2Ma),high values of all the CA species (S(CA))and individuals and diversity (H (CA))dominate over low values of all of the TH species (S(TH))and individuals and diversity (H (TH)).A prominent feature of this zone is that high values of S(CA),H (CA),CA mollusk individuals,S(TH)and H (TH),as well as total mollusk species and individuals,occur at around 70m depth,at the very base of the sequence;however,these values then decrease upwards.H (CA)and H (total)remain at high levels throughout the zone,and the equitability (E)of total species is also higher than in the other zones.

In Zone 2,from 56.8–34.8m depth (,6.2–5.4Ma),the total number of CA species and individuals remains at a similarly high level as in the previous zone,except for the interval from 42to 38m.In contrast,the total number of TH species and individuals is slightly higher than in the previous zone.The total number of species and individuals of all of the species (CA and TH combined)are generally higher than in the previous zone but with a decreasing trend.The diversity of all species,H (total),does not exhibit significant changes compared to Zone 1,and E(total)is somewhat lower than in Zone 1.

Zone 3,from 34.8–16.2m depth (,5.4–4.4Ma),is character-ized by low numbers of CA species and individuals being almost absent in the upper part,from 24m to 16.2m.This pattern of variation is paralleled by a clear increase of all the TH indices,including diversity.The total number of species and individuals of all of the species is lower than in Zone 2,except for the interval from about 32to 28m.There are no large magnitude changes in H (total)and E(total)within the zone.

Zone 4corresponds to the depth from 16.2m to the top of the sequence (,4.4to 3.5Ma).The number of CA species and individuals increases markedly and maintains relatively high values throughout the zone.The TH indices exhibit high values from about 16.2to 9m and then decrease significantly to very

low

Figure 3.Variations in terrestrial mollusks versus depth in the Dongwan sequence.Lithology and total mollusk individuals are from Li et al.,(2006a)[58]and Li et al.(2008)[47].S(CA)–Total number of species of the cold-aridiphilous (CA)mollusk group.H (CA)–Diversity of the CA mollusk group.S(TH)–Total number of species of the thermo-humidiphilous (TH)mollusk group.H (TH)–Diversity of the TH mollusk group.S(total)–Total number of species of the total mollusk group.H (total)–Diversity of the total mollusk group.E(total)–Equitability of the total mollusk group.doi:10.1371/journal.pone.0095754.g003

values up to4m,and increase again above about4m depth.All of the indices for all species,i.e.,S(total),H(total),and E(total), increase markedly;however,H(total)and E(total)exhibit a generally declining trend,implying that the diversity of the terrestrial mollusk populations decreased and that the distribution of individuals of different species was uneven.The total mollusk individuals in this zone is high and remains relatively stable except for the interval between8and4m,a pattern which differs from the other three zones where the total number of mollusk individuals is high at the beginning of the zone and then declines thereafter.

Moreover,the variation in diversity of the CA and TH ecological groups from the entire Dongwan sequence,as exhibited in Figure3,can be differentiated into two major intervals based solely on the Shannon index of the CA and TH groups;and this result probably reflects different ecological population dynamics. First,from the base of the Dongwan sequence to34.8m depth,the CA group is dominant,exhibiting high diversity with H values varying between0and1.75(mean of0.52).In contrast,the diversity of the TH populations exhibits significantly low values, ranging from0to1.58(mean of0.18)within this depth interval, although the diversity of all mollusk species,i.e.the sum of CA and TH,does not exhibit any clear changes.Second,from34.8m depth to the top of the sequence,the diversity of the CA group declines significantly with H values varying between0and1.56 (mean of0.14);and in contrast the TH group becomes dominant in terms of diversity with H values ranging from0to2.64(mean of 0.64).The diversity and equitability of all mollusk species also exhibit a significant change at about16.2m depth within this interval.

Discussion

Late Miocene and Pliocene Paleoclimatic Evolution in the Western CLP

Previous studies of European and North American Quaternary terrestrial mollusks have shown that mollusk assemblages,based not only on the occurrence of characteristic species but also on the statistical dispersion of the assemblages(e.g.,diversity,as described by the Shannon index(H)),can provide information about climatic conditions and mollusk populations[65–67].For example, correlation of terrestrial mollusk groups with changes in dust flux, and thus climatic conditions,has previously been observed in the European Quaternary terrestrial mollusk diversity record[65]. Here we use the Dongwan terrestrial mollusk record to extend the statistical analysis of terrestrial mollusk populations and the interpretation of climatic changes to the Late Neogene.As shown in Figure4,four stages can be recognized according to changes in the mollusk indices used in the present study,and which outline the evolutionary history of ecological and climatic conditions in the CLP from7.1to3.5Ma.

First,from7.1to6.2Ma(Zone1),the total number of CA species(S(CA))and diversity(H(CA))index are high;however,the number of CA mollusk individuals is generally low apart from a large high peak at around7Ma and which indicates diversified CA species.Conversely,all of the indices of the TH species exhibit low values except for the peak at around7Ma,indicating low diversity.These features may be related to the occurrence of very cold,dry climatic conditions,the occurrence of which is roughly coincident with the expansion of C4vegetation in the northeastern CLP[27],Central Inner Mongolia(Tunggur Area,Xilinhot Area, and Huade Area)[68](Figure1),and Pakistan[2].They also indicate the occurrence of seasons with water stress for vegetation and terrestrial mollusks as well as the fact that relatively dry climatic conditions had already appeared in northern China during the Late Miocene,coincident in age with the global transition from C3to C4vegetation[4].The occurrence of C4 plants during the latest Miocene should have been restricted to limited areas within deserts,and the occurrence of these niches could be coincident with,or occurred after,major uplift of the Tibetan Plateau at about8Ma[3,8,10,11].However,C4 vegetation was not yet to develop in the central and southern CLP,demonstrating that C3plants were still dominant as indicated by d13C values of soil carbonate in the Lingtai,Xifeng and Liantian Red Clay sequences in the eastern CLP[6,9,24]. This is also evidenced by the thickness of loess layers in the studied Dongwan sequence and by dust mass accumulation rates in the western Pacific.High dust deposition rates with a gradually increasing trend culminated at about6.2Ma in the western Pacific [69],corresponding to thicker loess layers in the Dongwan sequence(Figure4).Both features indicate drier climatic conditions in the Asian interior,the potential source region of dust deposits in the CLP and western Pacific.While dust accumulation in the western Pacific reached a maximum from about 6.5to 6.2Ma,the number of mollusk species and individuals at Dongwan was very low,implying very dry climatic conditions which were unsuitable even for the development of CA species.Pedostratigraphy and iron geochemistry of the Lingtai Red Clay deposits in the CLP indicate that the EA summer monsoon was relatively weak from7.05to6.2Ma[20,21].The d13C values of fossil enamel from a diverse group of herbivores and of paleosol carbonate and organic matter from the Linxia Basin indicate that C4grasses were either absent or insignificant in the Linxia Basin prior to,2–3Ma,suggesting that the East Asian summer monsoon was probably not strong enough to affect this part of China throughout much of the Neogene[28]. However,during our studied interval there is much evidence for a strong summer monsoon,evidenced mainly from mammal assemblages as well as analyses of mammal tooth and soil carbonate isotopes[22–25,27].Hypsodonty analysis of fossil mammals indicates that northern China became more humid at 7–8Ma,coincident with the previously recognized onset of Red Clay deposition in the eastern CLP,and which was interpreted by the authors as reflecting the onset or intensification of summer monsoonal precipitation[22,23].Soil carbonate isotopes from the Lantian fluvial and Red Clay deposits indicate the absence of any marked change in plant photosynthetic pathway or climate, implying the occurrence of pure C3vegetation with no indications of any C4plants during the Late Miocene and Pliocene.A general rise in d18O values probably reflects increased summer precipi-tation related to the onset and/or intensification of the Asian monsoon system[24,25],which is supported by a mammalian faunal turnover event implying a marked change to more humid and closed habitats[26].A strong summer monsoon at7.1–6.2Ma is also supported by the records of clay/feldspar ratio, kaolinite/chlorite ratio and biogenic opal mass accumulation rates (MAR)from the SCS,although the authors emphasize that their study is a schematic reconstruction which only outlines several principal stages and neglects the details[33].

There is also much evidence for a weakening of the summer monsoon and strengthening of the winter monsoon during the Late Miocene.The EA summer monsoon weakened after7.5Ma as evidenced by combined planktonic foraminifera Mg/Ca and d18O records from Ocean Drilling Program(ODP)Site1146, northern SCS[30].Radiolarian species numbers and individuals and diversity from ODP Site1143,southern SCS,suggest a summer monsoon maximum at8.24Ma and a major decline after 7.70Ma[32].Geochemical records from the ODP Site1148,

northern SCS,indicate that chemical weathering intensity decreased after the early Miocene with a rapid decrease centering at 7.2Ma,compatible with a weakening of the EA summer monsoon [31].The trend of increasing black carbon concentration and accumulation rate at ODP Site 1148suggests the progressive development of the East Asian winter monsoon after about 7Ma [29].In addition,grain-size evidence from the Linxia Basin of the CLP indicates that the EA winter monsoon intensified after 7.4Ma and again at 5.3Ma [19].

Thus it is noteworthy that the TH mollusks at Dongwan do exhibit peak values at around 7Ma,suggesting warm,humid climatic conditions consistent with a mammalian faunal turnover event [26];however,the peak does not extend to the subsequent period,implying that the interval of relatively warm and humid climate may have been a relatively brief event within the context of an overall very cold and arid climate.In addition,a recent synthesis of isotopic and sedimentological analyses,climate modeling and an extensive mesowear analysis of the Baode Red Clay sequence indicates that the climate at 7.5Ma was more humid than during the youngest interval at 5.7Ma and that variable climatic conditions occurred at ,6.5Ma.Thus a significant decrease in the EA summer monsoon strength from 7–5.7Ma in the Baode region,based on three samples dated at 7.0,6.5,and 5.7Ma [70],does not contradict the mollusk results.We suggest that much more definitive results would have been obtained if a higher sampling density had been used.In addition,numerous paleoclimatologists regard the occurrence of Red Clay sequences as reflecting aridity or desertification and an intensified winter monsoon [16,37,42,43,69,71],which contradicts the mammal and isotope record.

We suggest four possible reasons for the discrepancies amongst the extant research results.First,the sensitivity of the proxies used may be one of the main reasons;and indeed,it has long been found in Quaternary loess studies that different climatic proxies can respond differently to climatic changes [55].Second,as summarized by Wang et al.(2005)[72]and Kaakinen et al.(2006)

[24],interpretations of expansions of C4vegetation are conten-tious in terms of whether or not they are a summer monsoon proxy [2,4,45].Third,regional difference in patterns of climate change may have occurred,as suggested by Passy et al.(2009)[27].Finally,low stratigraphic resolution may have resulted in the failure to resolve environmental changes in sufficient detail,and high resolution mammalian faunal studies (for example using a 20-cm interval)may shed light on the observed differences.In summary,the conflicts cannot be resolved by the present study and future studies employing more sensitive proxies,higher resolution or continuous sampling combined with accurate dating may be necessary.

Second,from 6.2to 5.4Ma (Zone 2),the dominant CA terrestrial mollusks indicate that the climate during this interval remained cold and dry,but was not drier than in Zone 1,as evidenced by the slightly greater abundance of TH species and individuals.At the beginning of this zone,from about 6.2to 5.8Ma,the number of TH mollusk individuals was higher,and this corresponds to a declining rate of dust deposition as indicated by the thinness of the loess layers in the Dongwan sequence (Figure 4).This supports the finding that decreasing or increasing dust deposition affects the development of terrestrial mollusks by creating either more-or less-favorable environmental conditions [65].After about 5.8Ma the number of TH mollusk individuals was reduced,which is probably related to the increase of dust deposition in the CLP,as shown by the increased thickness of the loess represented by this interval (Figure 4).These cold,dry climatic conditions were not solely restricted to the western CLP;in the eastern CLP,mollusks in the Xifeng Red Clay sequence exhibit dominant percentages of the CA group associated with a few meso-xerophilous components and a lesser occurrence of TH species,also indicating a cold,dry climate [46].This is also reflected by the coarse grain size of the Red Clay sequence in the CLP [16],and by the fact that dust deposition rates in the western Pacific remained high,albeit lower than before,and with a declining trend towards the subsequent time interval from 5.4

and

Figure 4.Variations in the terrestrial mollusks of the Dongwan sequence in the western CLP from 7.1to 3.5Ma,and comparison with other climate proxies.The proxies are d 13C of soil carbonate (d 13C SC )in the Lingtai Red Clay sequence [6],loess and soil thickness in the Dongwan sequence (this study),global cooling trend deduced from the marine benthic foraminiferal d 18O record [1],and continental aridity inferred from the mass accumulation rate (MAR)of eolian dust at ODP Site 885/886in the western Pacific [69].Geomagnetic polarity chronology and age of the Dongwan sequence is from Hao and Guo (2004)[41].S(CA)–Total species of the cold-aridiphilous (CA)mollusk group.H (CA)–Diversity of the CA mollusk group.S(TH)–Total number of species of the thermo-humidiphilous (TH)mollusk group.H (TH)–Diversity of the TH mollusk group.doi:10.1371/journal.pone.0095754.g004

4.4Ma[69].The thickness of the Dongwan loess layers was not higher than before,except at about6.2and

5.6Ma;however,the thickness of the soil layers does not change significantly.The d13C values of the soil carbonates in the Lingtai and Xifeng Red Clay sequences were similar to those of the previous time interval from 7.1to

6.2Ma,indicating again that C4plants were not the dominant vegetation in the studied area of the CLP[6,9].These lines of evidence indicate generally cold,dry climatic conditions in the EA continent but which were not drier than the lower stage. However,the global mean benthic foraminiferal d18O record demonstrates that global ice volume was increasing with the highest values occurring at about 5.8–5.7Ma,followed by a decrease towards the upper stage[1].

There is much evidence supporting the conclusion from the Dongwan mollusk results that the winter monsoon may still have been strong from 6.2–5.4Ma but that the summer monsoon strengthens than before although may be to a lesser extent,as confirmed by the pedostratigraphy and iron geochemistry of the Lingtai Red Clay deposits in the CLP[20,21].The coeval pollen record from the Lingtai section exhibits a predominance of Chenopodiaceae and Artemisia,indicating a desert or desert-grassland landscape during the Late Miocene[73].A higher dust accumulation rate and coarser eolian grain size in the CLP and in the North Pacific suggest stronger continental aridity in the Asian interior from,6.2to,5Ma[14,16,69].The variation in the U-ratio of the grain size of the Red Clay,reflecting the changing strength of the winter monsoon,indicates a strong winter monsoon between6.1and5.4Ma[13].The sedimentation rate across the CLP,including at the Baode Red Clay sequence,indicates that the EA winter monsoon strengthened between6.26and5.4–5.25Ma [14,15].

Third,from5.4to4.4Ma(Zone3),the prominent feature is that all of the CA species and individuals are very few in number and in fact they decrease significantly with almost no occurrence after about5Ma.In contrast,there are high values of the TH species numbers and individuals with the maxima occurring at around5–5.1Ma when a thick soil layer formed,indicating warm, moist climatic conditions.In the eastern CLP,the mollusk fauna was characterized by maximum abundance of TH species,an absence of CA species,and relatively abundant meso-xerophilous taxa[46].The Xifeng pollen record indicates a significant increase of temperate forest plants,also implying humid regional climatic conditions during this period[74].The d13C values indicate a slight decrease and thus a shift towards more C3plants in the CLP in agreement with the pollen results(Figure4).Ding et al.(1999) identify extremely mature soils in the5.5–3.85Ma interval at Lingtai,and interpret these as indicating warm and wet climates, and possibly the strongest summer monsoons in the past7Ma [20].Minimum grain size and sedimentation rate in the CLP [15,16],decreased thickness of loess layers in the Dongwan sequence(Figure4),and very low dust deposition rates in the western Pacific[69]together suggest very warm,moist climatic conditions in the CLP and less dry conditions in the Asian interior, the potential source area of dust in the CLP and western Pacific. However,this warm climate is not clearly recorded by the global mean benthic foraminiferal d18O record compiled by Zachos et al. (2001)[1].

Last,from4.4to3.5Ma(Zone4),all of the CA indices increase significantly and remain almost unchanged,while in contrast all of the TH indices exhibit a different pattern of variability with high values from4.4to4.0Ma,coincident with changes in the CA indices,an abrupt decrease from4.0Ma and increased values again from3.7Ma.The CA species during this time interval were different from those between7.1and5.4Ma.Indeed,the CA species of Cathaica pulveraticula,Cathaica schensiensis,and Pupopsis retrodens have only been identified in this zone,as shown by Li et al. (2006a)[58],probably indicating that climatic conditions became drier.The coeval Xifeng land snail record from the eastern CLP is dominated by meso-xerophilous taxa,associated with a signifi-cantly reduced abundance of TH species and the paucity of CA taxa during the late period[46].Pollen data from the Xifeng Red Clay sequence indicate a typical steppe ecosystem during this period[74].These variations are in good agreement with the expansion of C4plants in the central CLP as observed at the Lingtai and Xifeng Red Clay sequences[6,9].In addition,the loess layers in the Dongwan section during this time interval are of moderate thickness,thinner than from7.1to6.2Ma but thicker than from5.4to4.4Ma.In contrast the paleosols are somewhat thicker than before(Figure4),indicating longer pedogenesis under different climate conditions,and probably enhanced seasonality, corresponding to expansions of C4plants in the central CLP[6,9]. Pedostratigraphy and iron geochemistry of the Lingtai Red Clay deposits in the CLP indicate that the EA summer monsoon weakened significantly over the interval3.85to3.15Ma[20,21]. Dust deposition increased again in the Pacific in parallel with increased aridity in the dust source areas[69](Figure4). Moreover,the entire Dongwan terrestrial mollusk record provides information about the evolution of mollusk diversity and climatic changes from the Late Miocene to the Pliocene. Previous studies indicate that in most Quaternary loess sequences in Europe and North America generally fewer than20mollusk species can be identified and diversity varies with H values between0and4,suggesting that the loess deposits provided few additional ecological niches for land snails to grow and develop [65–67].In the Neogene Dongwan loess sequence in the CLP, East Asia,24mollusk species were identified and diversity varies between0and2.5,which also suggests that fewer niches were provided.The response of the Neogene terrestrial mollusk populations to climatic changes depends on their ecological requirements.Different ecological groups,such as CA and TH, respond differently.During the time interval from7.1to5.4Ma when a cold,dry climate obtained,as indicated by a high flux of dust in the CLP and western Pacific,the diversity of the CA group was high,indicating that relatively cold,dry climatic conditions may be favorable for the development of CA terrestrial mollusk populations.In contrast,during the relatively warm,moist time interval from5.4to4.4Ma,corresponding to a reduced loess thickness in the CLP and low dust flux in the western Pacific,the diversity of the TH terrestrial mollusk populations was high. Possible Causes of Paleoecological and Paleoclimatic Evolution in the Western CLP during the Late Miocene and Pliocene

Dust in the Asian interior,including northwestern China,was emitted and transported in two possible modes,corresponding to patterns of low and high level atmospheric circulation.One mode is that the Asian dust was transported eastwards by high atmospheric circulations(westerlies)and reached northwestern Pacific,as recorded by high values of dust flux to the northwestern Pacific.The other mode is that dust in the Asia interior was transported by low level atmospheric circulation,the EA winter monsoon,to the middle reaches of the Yellow River,leading to the formation of the CLP[37,49,75,76].Thus loess sequences in the CLP and dust deposits in the western Pacific both relate to climatic changes that impacted the regions to the north of the Tibetan Plateau,i.e.,the Asian interior,as has been indicated by the previous studies of Hovan et al.,(1989)[77]and Rea et al.,(1998) [69].

At approximately8–7Ma,the accumulation rate of eolian deposits in the CLP reached high values of about4cm/ka[37] and dust deposition in the western Pacific was maximal[69] (Figure4),indicating that particularly dry climatic conditions must have prevailed in the Asian interior resulting in the mobilization and transport of large amounts of dust.Indeed,a palynological study of the Late Miocene–Pliocene sediments of the Dushanzi section from northwestern China(Figure1)indicates that steppe taxa(Artemisia and Chenopodiaceae)were generally dominant, implying that a dry climate existed in the inland basins of northwestern China since8.7Ma,except for a warm and humid phase that lasted from5.8to3.9Ma[78].In addition,significant desertification in northwestern China prevailed as early as7.2–7Ma,as shown by the development of eolian sand dunes in the Taklimakan Desert[79]and eolian Red Clay deposition around the Lanzhou region[80].These climatic and environmental conditions probably provided a suitable environment for the growth and development of C4plants in northern China and promoted the expansion of eolian deposits from the west towards the eastern part of the CLP[42,43]and which constituted suitable environments for terrestrial mollusks.Thus terrestrial mollusks grew and developed in the CLP and were able to record the patterns of environmental evolution as recorded by the Dongwan sequence.

Variations in the Dongwan terrestrial mollusk assemblages indicate that,during the time interval from7.1to3.5Ma,major paleoecological and paleoclimatic changes occurred at about6.2, 5.4,and4.4Ma.The change at around6.2Ma,the boundary between Zones1and2,is less significant than the one at4.4Ma, and therefore it is not clearly reflected in terms of a transition in periodicity recorded by the relative abundance of mollusks at this time[47].Indeed,a relatively high number of CA mollusk species and individuals,consistent with the high relative abundance of CA mollusks[47],prevailed during Zone1and Zone2,indicating that a cold,arid climate prevailed in the study area.These two zones exhibit the same dominant100kyr periodicity[47],again suggesting that the6.2Ma datum was not particularly significant at Dongwan.However,the TH mollusk individuals and species are somewhat different within these two zones,and in addition the appearance of mollusks in the Xifeng Red Clay sequence and the upper age of the QA-I section imply that6.2Ma may be an important datum in the paleoclimatic evolution of the CLP [37,46].

Changes in the CA mollusks of Zones1and2are paralleled by a global cooling trend[1](Figure4),increased ice-rafted detrital flux in the Northern Hemisphere[81–85],and the buildup of the Western Antarctic ice sheet[1].The CLP is particularly sensitive to changes in high northern latitudes through the EA winter monsoon circulation[76,86].Extended ice sheets in the Northern Hemisphere reinforce the southward movement of cold air and thereby enhance the Siberian High that controls the EA winter monsoon wind system[86].Thus,global cooling,especially the expansion of ice deposits in high northern latitudes,could have affected the Siberian High and the EA winter monsoon,thereby expanding habitats for the CA mollusks in the CLP.

There is no evidence for major uplift of the Tibetan Plateau at about6.2Ma,and therefore this mechanism is excluded as a cause of the change at this time.However,if the Tibetan Plateau reached a significant height at about8Ma it would have accelerated climatic cooling and strengthened the EA winter monsoon[3,8,87–90],causing cold,dry climatic conditions in the western CLP during the Late Miocene,as discussed above.

The shift at about5.3–5.4Ma roughly corresponds to the onset of the Pliocene when global climate became warmer than before.However,the climatic drivers contributing to the Pliocene global warming are still highly debated.As summarized by Haywood et al.(2009)[91],possible candidates include paleogeographic changes[92],altered atmospheric trace gas concentrations and water vapor content[93],changes in oceanic circulation[94,95], oceanic heat transport[5,96],thermal structure of the oceans[97–99],and feedbacks generated through altered land cover (including ice sheet extent),surface albedo,cloud cover and temperature[100].

Our results seem to support the suggestion that the warming interval may be related to changes in ocean circulation and ocean heat transport caused by the closures of the Panama and Indonesian seaways[5,94–96].Closure of these two seaways may have caused changes in heat distribution between the Pacific and Atlantic,causing reorganization of global climatic patterns and changing the pattern of atmospheric moisture flux from latitudinal to meridional,resulting in increased moisture flux to high latitudes[5,95,101]and contributing to climate changes in the CLP.Moreover,both geological records and modeling studies show that closures of the Panama and Indonesian seaways likely played important roles in the strengthening and enlargement of the western Pacific warm pool[5,102–106],providing more moisture and heat to the CLP favorable for the abundant occurrence of TH mollusk species.

The4.4Ma shift,representing a climatic transition from early Pliocene warming to late Pliocene cooling,is observed in the Dongwan mollusk diversity and species numbers and individuals; however,it is not clearly shown in the relative abundance of mollusks[47].It may be related to tectonic events such as the uplift of Tibetan Plateau,since climate models suggest that uplift played a particularly important role in the evolution of the global paleoenvironment[8,87–90],and the effects of which on the EA winter monsoon are more significant than on the summer monsoon[89].Changes in depositional facies from distal alluvial plains to proximal alluvial fans and an increase in sedimentation rate near Yecheng(Figure1)in the western Kunlun Mountains indicate the uplift of the northern Tibetan Plateau at about 4.5Ma[7].This tectonic activity is thought to trigger not only the enhancement of the EA monsoon,but is also considered to be a driver of general cooling through the consequent increase in the rate of chemical weathering,thus accelerating ice expansion in Northern Hemisphere high latitudes[88,107,108]and further strengthening the Siberian High and the EA winter monsoon and transportation of dust to the CLP.Furthermore,uplift of the Tibetan Plateau could have blocked moisture transport to the Asian interior,contributing to its aridification.Under these climatic conditions,the northern CLP would have commenced a drying trend earlier than the southern CLP,causing significant ecological changes in terrestrial ecosystems including terrestrial mollusks and C4plants at roughly4.4Ma.

Conclusions

The Dongwan terrestrial mollusk record from the western CLP exhibits four stages during the time interval from7.1to3.5Ma, indicating the phased evolution of paleoecology and paleoclimate. From7.1to 6.2Ma,very cold and dry climatic conditions prevailed.From6.2to5.4Ma,the climate remained cold and dry but was not as dry as the preceding interval,as evidenced by the dominance of CA mollusks and rather more TH species and individuals.From5.4to4.4Ma,very warm and moist climatic conditions prevailed,evidenced by high values of the TH species and individuals,as well as by the very small numbers of CA species and individuals and their almost complete absence after about

5Ma.From 4.4to 3.5Ma,all of the CA indices increase significantly and remain at a high level,indicating a cooling climate;however,all of the TH indices exhibit relatively high valuesfrom4.4to4.0Ma,an abrupt decrease from4.0Ma and an increase again from 3.7Ma.The three CA species,Cathaica pulveraticula,Cathaica schensiensis,Pupopsis retrodens,occurred solely during this period and were absent from7.1to5.4Ma,suggesting that the climate from4.4to3.5Ma was becoming colder and drier than previous stage.

The very cold and arid climatic conditions,with changes at about6.2Ma,are paralleled by a global cooling trend,increased in ice-rafted detrital flux in the Northern Hemisphere[81–85], and the buildup of the Western Antarctica ice sheet[1].The shift at about5.3–5.4Ma roughly corresponds to the onset of the Pliocene when global climate became increasingly warmer than previously.Our results seem to support the suggestion that the warming interval may be related to changes in oceanic circulation and oceanic heat transport[5,94–96].The4.4Ma shift may be related to tectonic events such as the uplift of Tibetan Plateau. Variations in the diversity of the CA and TH mollusks,H(CA) and H(TH),are closely related to climatic changes during the Late Miocene to Pliocene.From7.1to5.4Ma when a cold,dry climate prevailed,the CA group was the more diverse.In contrast,during the relatively warm,wet time interval from5.4to4.4Ma,the TH terrestrial mollusk populations became more diverse.It should be pointed out that most of the Neogene terrestrial mollusks in the CLP have modern representatives and therefore they have the potential to estimate quantitatively Neogene changes in temper-ature and precipitation in the CLP.However,such estimates depend upon the development of a training set based on a large number of surface samples.Changes in fossil terrestrial mollusk diversity are significant for the prediction of terrestrial biodiversity changes,and Quaternary loess deposits in Europe and North America have been studied in this context.The22-Ma loess deposits in China provide an excellent opportunity for under-standing long term changes in terrestrial mollusk diversity;and although the present paper focuses on the Late Neogene terrestrial mollusk in the CLP,ongoing studies will focus on other time intervals.

Supporting Information

Table S1The depth,age,and mollusk data from the Dongwan loess-paleosol sequence.S(CA)–Total number of species of the cold-aridiphilous(CA)mollusk group.H(CA)–Diversity of the CA mollusk group.CAMI–Mollusk individuals of the CA mollusk group.S(TH)–Total number of species of the thermo-humidiphilous(TH)mollusk group.H(TH)–Diversity of the TH mollusk group.THMI–Mollusk individuals of the TH mollusk group.S(total)–Total number of species of the total mollusk group.H(total)–Diversity of the total mollusk group. E(total)–Equitability of the total mollusk group.TMI–Total Mollusk individuals.

(XLS)

Acknowledgments

We thank all of the reviewers for valuable comments,criticisms and suggestions.We are grateful to Dr.Jan Bloemendal for editing the English and for suggestions,Prof.Qingzhen Hao for field assistance and Prof. Shiling Yang for providing us with d13C data of soil carbonates from the Lingtai Red Clay sequence.

Author Contributions

Conceived and designed the experiments:FL NW.Performed the experiments:FL NW YP.Analyzed the data:FL NW DDR YD DZ. Contributed reagents/materials/analysis tools:FL NW.Wrote the paper: FL NW DDR.

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英语单词惯用法集锦解析

英语单词惯用法集锦 习惯接动词不定式的动词（V to inf) adore(vi极喜欢) dread （vt.不愿做，厌恶）plan 计划 afford（+to,vt有条件，能承担）endeavour （vt，竭力做到，试图或力图）prefer（vt.宁可；宁愿(选择)；更喜欢）agree 同意endure(忍受.cannot ~ to) prepare准备 aim (vi[口语]打算：) engage (vi.保证，担保；) presume(vt.冒昧；敢于[用于第一人称时为客套话]：) appear (vi.似乎；显得) essay(vt.尝试，试图) pretend(vt.自命；自称；敢于；妄为) apply （申请）expect（期望，希望）proceed（开始，着手，）arrange （vi.做安排，(事先)筹划）fail （vt.未做…；疏忽)promise(许诺，保证做 ask （要求）forget （vt. 忘记）purpose （vt.决心，打算） beg （vt.正式场合的礼貌用语]请(原谅)，请(允许)：I beg to differ.恕我不能赞同）guarantee（保证，担保）refuse（拒绝）bear 承受，忍受hate（[口语]不喜欢；不愿意；）regret （vt. 抱歉；遗憾）begin help （有助于，促进）remember（记住） bother （vi.通常用于否定句]麻烦，费心）hesitate（vi.犹豫；有疑虑，不愿）scheme（策划做）care （vt.想要；希望；欲望[后接不定式，常用于否定、疑问及条件句中]）hope （vt.希望，盼望，期待）seek（vt.谋求，图谋[后接不定式]） cease （停止; 不再(做某事)[正式] intend （打算；想要）seem（似乎，好像[后接不定式或从句]；觉得像是，以为[ choose （意愿；选定；决定）itch start开始claim （vt. 主张；断言；宣称） continue （继续）like 喜欢swear（vt.起誓保证；立誓要做(或遵守） dare （vt.敢，敢于，勇于，胆敢）long（vi.渴望；热望；极想） decline（vt.拒绝，拒不(做、进入、考虑等) manage（设法完成某事）threaten（vt.威胁，恐吓，恫吓）deign （屈尊做）mean（有意[不用进行时）trouble（vi.费心，费神；麻烦）demand（vi.要求，请求：）need （需要）try（设法做） deserve (应得) neglect (疏忽) undertake(承诺,答应，保证) desire （希望渴望）offer（表示愿意(做某事)，自愿；）venture（冒险(做某事））determine（vi.决心，决意，决定，）omit （疏忽，忘记）want 想要 die （誓死做）pine （渴望）wish （希望） 习惯接“疑问词+动词不定式”的动词（有时也包括VN wh-+to do) advise 建议explain 解释perceive 觉察，发觉 answer 答复find 得知，察觉persuade 说服，劝说；使某人相信 ask 询问，问forget 忘记phone 打电话 assure 保证guess 臆测，猜度pray 祈祷 beg 请求，恳求hear 小心聆听（法庭案件）promise 允诺 conceive 想象，设想imagine 以为，假象remember记得 consider 考虑，思考indicate 暗示remind 提醒，使想起 convince 使相信inform告知通知instruct告知，教导 see 看看，考虑，注意decide 解决，决定know 学得，得知 show 给人解释；示范；叙述；discover发现；知道learn 得知，获悉 signal以信号表示doubt 怀疑，不相信look 察看；检查；探明 strike 使想起；使突然想到；使认为suggest 提议，建议tell 显示，表明；看出，晓得；warn 警告，告诫think 想出；记忆，回忆；想出，明白wonder 纳闷，想知道 wire 打电报telegraph 打电报 习惯接动名词的动词（包括v+one’s/one+v+ing) acknowledge 认知，承认…之事实escape免除，避免omit疏忽，忽略 admit 承认，供认excuse 原谅overlook 放任，宽容，忽视adore （非正式）极为喜欢fancy 构想，幻想，想想postpone 延期，搁置 advise 劝告，建议finish完成prefer较喜欢 appreciate 为…表示感激(或感谢)forbid 不许，禁止prevent预防 avoid 逃避forget 忘记prohibit 禁止，妨碍

“的、地、得”用法分析及练习(后附答案)

“的、地、得”用法分析及练习（后附答案） 一、的、地、得用法分析： “的”后面跟的都是表示事物名称的词或词语，如：敬爱的总理、慈祥的老人、戴帽子的男孩、珍贵的教科书、鸟的天堂、伟大的祖国、有趣的情节、优雅的环境、可疑的情况、团结友爱的集体、他的妈妈、可爱的花儿、谁的橡皮、清清的河水...... “地”后面跟的都是表示动作的词或词语，如：高声地喊、愉快地唱、拼命地逃、疯狂地咒骂、严密地注视、一次又一次地握手、迅速地包围、沙沙地直响、斩钉截铁地说、从容不迫地申述、用力地踢、仔细地看、开心地笑笑......” “得”前面多数是表示动作的词或词语，少数是形容词；后面跟的都是形容事物状态的词或词语，表示怎么怎么样的，如：走得很快、踩得稀烂、疼得直叫唤、瘦得皮包骨头、红得发紫、气得双脚直跳、理解得十分深刻、乐得合不拢嘴、惊讶得目瞪口呆、大得很、扫得真干净、笑得多甜啊...... 二、的、地、得用法补充说明： 1、如果“de”的后面是“很、真、太”等这些词，十有八九用“得”。 2、有一种情况，如“他高兴得一蹦三尺高”这句话里，后面的“一蹦三尺高”虽然是表示动作的，但是它是来形容“高兴”的程度的，所以也应该用“得”。

三、的、地、得用法总结： 1、“的”前面的词语一般用来修饰、限制“的”后面的事物，说明“的”后面的事物怎么样。结构形式一般为：修饰、限制的词语+的+名词。 2、“地”前面的词语一般用来形容“地”后面的动作，说明“地”后面的动作怎么样。结构方式一般为：修饰、限制的词语+地+动词。 3、“得”后面的词语一般用来补充说明“得”前面的动作怎么样，结构形式一般为：动词（形容词）+得+补充、说明的词语。 四、的、地、得用法例句： 1. 蔚蓝色的海洋，波涛汹涌，无边无际。 2. 向日葵在微风中向我们轻轻地点头微笑。 3. 小明在海安儿童公园玩得很开心。 五、“的、地、得”的读音： “的、地、得”是现代汉语中高频度使用的三个结构助词，都起着连接作用；它们在普通话中都各自有着各自的不同的读音，但当他们附着在词，短语，句子的前面或后面，表示结构关系或某些附加意义的时候都读轻声“de”，没有语音上的区别。 但在书面语中有必要写成三个不同的字，这样可以区分他们在书面语用法上的不同。这样做的好处，就是可使书面语言精确化。

常见动词用法

1、keep ①keep + 形容词表示“保持” Please keep quite. 请保持安静。 ②keep + 宾语+ 形容词（或介词短语）表示“把……保持在某一状态” We must do everything we can to keep the air clean. 我们必须尽一切所能保持空气清洁。 ③keep sb doing sth 表示“让某人做某事” ——只能用现在分词作宾语补足语，不能用不定式。 He kept us waiting for two hours. 他让我们等了两个小时。 He kept us to wait for two hours. (错误) ④keep on doing sth和keep doing sth 表示“继续做某事，反复做某事”，可换用。 但keep on doing 更强调动作的反复性或做事人的决心。 He keeps on phoning me, but I don’t want to talk to him. Though he failed 3 times, he kept on trying. 他老是给我打电话，但我不想同他讲话。虽然他已失败了3次，但他仍继续干下去。 keep doing sth 经常用于静态动词。 He kept lying in bed all day long. 他整天都躺在床上。 ⑤keep …from doing sth 表示“阻止，使免于” He kept them from fishing in the lake. 他不让他们在那个湖里捕鱼。 2、may not / mustn’t / needn’t / wouldn’t ①may not be 是may be的否定式，意为“可能不是，也许不是” He may be there.他可能在那里。He may not be there.他可能不在那里。 ②must 意为“必须”，mustn’t 意为“千万不可，绝对不可” 所以Must we/I ……?的否定回答要用needn’t—意为“不必” -Must we get there before 11 o’clock？ -No, we needn’t. ③wouldn’t = would not 意为“不会，不愿” I wouldn’t say no. 3、do ①do表示“做”，做某事，常指某种不具体的活动；make表示“制作”，指做出某种具体的东西。

常见蛋白质分子量参考值

常见蛋白质分子量参考值（单位：dalton） 蛋白质分子量 肌球蛋白[myosin] 甲状腺球蛋白[thyroglobulin] β-半乳糖苷酶[β-galactosidase] 副肌球蛋白[paramyosin] 磷酸化酶a[phosphorylase a] 血清白蛋白[serum albumin] L-氨基酸氧化酶[L-amino acid oxidase] 地氧化氢酶[catalase] 丙酮酸激活酶[pyruvate kinase] 谷氨酸脱氢酶[glutamate dehydrogenase] 亮氨酸氨肽酶[glutamae dehydrogenase] γ-球蛋白，H链[γ-globulin, H chain] 延胡索酸酶（反丁烯二酸酶）[fumarase] 卵白蛋白[ovalbumin] 醇脱氢酶（肝）[alcohol dehydrogenase (liver)]烯醇酶[enolase] 醛缩酶[aldolase] 肌酸激酶[creatine kinase]220,000 165,000 130,000 100,000 94,000 68,000 63,000 60,000 57,000 53,000 53,000 50,000 49,000 43,000 41,000 41,000 40,000 40,000

胃蛋白酶原[pepsinogen] D-氨基酸氧化酶[D-amino acid oxidase] 醇脱氢酶（酵母）[alcohol dehydrogenase (yeast)] 甘油醛磷酸脱氢酶[dlyceraldehyde phosphate dehydrogenase] 原肌球蛋白[tropomyosin] 乳酸脱氢酶[lactate dehydrgenase] 胃蛋白酶[pepsin] 转磷酸核糖基酶[phosphoribosyl transferase] 天冬氨酸氨甲酰转移酶，C链[aspertate transcarbamylase, C chain] 羧肽酶A[carboxypeptidase A] 碳酸酐酶[carbonic anhydrase] 枯草杆菌蛋白酶[subtilisin] γ-球蛋白，L链γ-blobulin,L chain[] 糜蛋白酶原（胰凝乳蛋白酶原）[chymotrypsinogen 胰蛋白酶[trypsin] 木瓜蛋白酶（羧甲基）[papain (carboxymethyl)] β-乳球蛋白[β-lactoglobulin] 烟草花叶病毒外壳蛋白（TWV外壳蛋白）[TWV coat protein 肌红蛋白[myoglobin] 天门冬氨酸氨甲酰转移酶，R链[aspartate transcarbamylase, R chain] 血红蛋白[h(a)emoglobin]40,000 37,000 37,000 36,000 36,000 36,000 35,000 35,000 34,000 34,000 29,000 27,600 23,500 25,700 23,300 23,000 18,400 17,500 17,200 17,000

Population用法

Population用法 population是一个集合名词（无复数形式)，它的用法有时较为特殊,所以很容易用错。 下面谈一下它的用法: 一、population常与定冠词the连用,作主语用时,谓语动词常用第三人称单数形式。 例如: The world\'s population is increasing faster and faster. 全世界的人口增长得越来越快。 At the beginning of the twentieth century, the world\'s population was about 1,700 million. 在二十世纪初,全世界的人口大约是十七亿。 二、当主语是表示\"人口的百分之几、几分之几\"时,谓语动词用复数形式。 例如: About seventy percent of the population in China are farmers. 中国大约有百分之七十的人口是农民。 三、有时population可用作可数名词,其前可用不定冠词。 例如: China has a population of about 1.3 billion. (=There is a population of about 1.3 billion in China.) 中国大约有十三亿人口。 New York is a big city with a population of over 10 million. 纽约是一个有一千多万人口的大城市。 在表示多个地区的人口时,population要用复数形式populations。 例如: Many parts of the world, which once had large populations and produced plenty of crops, have become deserts. 世界上很多地区一度人口众多,种植大量的农作物;现在,这些地区已经变成了沙漠。 四、表示人口的\"多\"或\"少\",不用\"much\"或\"little\",而要用\"large\"或\"small\"。 例如: India has a large population. 印度人口众多。 Singapore has a small population. 新加坡人口少。 五、询问某国、某地有多少人口时,不用\"How much...?\",而用\"How large...?\";在问具体人口时用\"What...?\" 例如: -How large is the population of your hometown? 你们家乡有多少人口? -The population of our hometown is nearly twice as large as that of yours. 我们家乡的人口是你们家乡人口的将近两倍。 -What is the population of Canada? 加拿大的人口有多少? -The population of Canada is about 29 million. 加拿大的人口大约有二千九百万。 六、population还表示\"某地、某类的动、植物或物品的总数\"。 例如: In India, however, the population of tigers has increased, from 2,000 in 1972 to about 5,000 in 1989. 然而在印度,老虎的总数已从1972年的2,000只增长到了1989年的大约5,000只。

动词以及动词短语的用法(动词后加to do 还是doing)

一动词加-ing 的情况 consider, suggest/advise,look forward to, excuse/pardon admit,delay/put off,fancy avoid,miss,keep/keep on,practise deny,finish,enjoy/appreciate forbid,imagine,risk can't help,mind,allow/permit,escape 考虑建议盼原谅, 承认推迟没得想. 避免错过继续练, 否认完成就欣赏. 禁止想象才冒险, 不禁介意准逃亡. 如：建议：advise,suggest,冒险:risk,献身:devote oneself to 二动词后加doing 和加to do sth. 意思不一样的情况 ①remember doing指记住过去做过的事，remember to do指记住将来要做的事，表示“不要忘记”。 ②forget doing表示忘记过去做过的事，forget to do表示“没有想起做某事”。 ③mean doing表示“意味着做某事”，mean to do表示“打算做某事”。 ④regret doing表示对已做过的事感到后悔，regret to do表示对将要做的事表示遗憾。 ⑤stop doing表示“停止做某事”，stop to do是停止做正在做的事以便去做另外一件事，这里的to do不是stop的宾语而是stop的目的状语。 ⑥try doing表示“尝试做某事”，try to do表示“设法、试图做某事”。 ⑦go on doing表示继续做同一件事，go on to do表示做完一件事后，接下去做另外一件事。 三动词后加to do sth. afford负担得起agree同意appear似乎，显得arrange安排 ask问attempt企图beg请求begin开始 choose选择claim要求decide决定demand要求 desire愿望determine决定expect期望fail不能 forget忘记happen碰巧hate憎恨，厌恶hesitate犹豫 hope希望intend想要learn学习long渴望 love爱manage设法mean意欲，打算need需要 neglect忽视offer提供omit忽略，漏other扰乱；烦恼

population 的用法

population 的用法 1.population 常以单数形式出现，意为“人口”“人数”。如果指世界不同地区的人口时，用复数。 （1）The population of this city is growing every year. (2) Many parts of the world, which once had large populations and produced plenty of crops, have become deserts. 2.做主语时，谓语动词的数的选用，population直接做主语，谓语动词一般用单数，前面有some, most 或者百分数时，谓语动词常用复数，前面有分数时，谓语动词单复数即可。 (1).The population is increasing faster and faster. (2).At the beginning of the twentieth century, the world\'s population was about 1,700 million. (3).About seventy percent of the population in China are farmers. (4).Most of the population of the city are workers. (5).One third of the population now smoke/smokes. 3.population 前的冠词的选用，population of 跟地名或者事物时，用定冠词the, population of 跟数词时，用不定冠词a, population 表示抽象意义时，用零冠词。 （1）.China has a population of about 1.3 billion. (2). New Y ork is a big city with a population of over 10 million. (3). The population of Canada is about 29 million. (4). The people’s living standard has risen, causing a rise in population. 4.询问某国、某地有多少人口时,不用\"How much...?\",而用\"How large...?\";在问具体人口时用\"What...?\"。表示人口的\"多\"或\"少\",不用\"much\"或\"little\",而要用\"large\"或\"small\" (1).How large is the population of your hometown? 你们家乡有多少人口? (2).The population of our hometown is nearly twice as large as that of yours. 我们家乡的人口是你们家乡人口的将近两倍。 (3).What is the population of Canada? 加拿大的人口有多少? 5. 在表示多个地区的人口时,population要用复数形式populations。例如: Many parts of the world, which once had large populations and produced plenty of crops, have become deserts. 世界上很多地区一度人口众多,种植大量的农作物;现在,这些地区已经变成了沙漠。

pretend三种易混淆不定式的用法

pretend三种易混淆不定式的用法 今天给大家带来了pretend三种易混淆不定式的用法，我们一起来学习吧，下面就和大家分享，来欣赏一下吧。 pretend三种易混淆不定式的用法 1. pretend to do sth .这个短语的意思是假装(将要)去做什么事情，适用于将来时态动作将来假装要去做但不一定去做的状态。 举例: If youpretend to know what you dont know，youll only make afool of yourself.不懂装懂就会闹笑话。(suri的回答) Child pretend to be mother and father in kindergarten.孩子在幼稚园里面假扮父亲和母亲(表将来)(JasoOon的回答) 2. pretend to have done sth .这个短语的意思是假装已经做过了某事，强调事情的一个完成的状态，侧重于假装的事情已经做好了。 举例:I pretend tohave seen nothing，but I cant.我假装自己没有看到任何东西，但是我做不到(侧重于一个完成时态，已经试图去假装没有看到)

she pretended to have finished the homeworkwhen she went out and played.当她出门玩的时候她假装自己已经完成了家庭作业。(假装做作业这个动作已经在出门玩之前做完了)(JasoOon的回答)以及怀陌的回答:When the teacher came in，he pretended to havefinished the homework.当老师进来的时候他假装自己已经完成家庭作业了，两者有异曲同工之妙。 3. pretendtobe doing sth 这个短语的意思是假装正在做某事，强调动作的一个进行时态。 举例:They pretend to be reading books when the teacher sneakingly stands at the back door.当老师偷偷地站在后门的时候他们假装正在读书(读书与老师站在后门都是过去进行时 态)(JasoOon的回答) Asmanypeople do，youoftenpretend to be doingwork when actuallyyou arejust wasting time online.像很多人一样，你经常假装正在工作，其实是在上网。 群主补充：昨天和今天已提交作业的同学，做得都很好，全部授予小红花。希望你们再接再厉，不要松懈哟。所以下周一出题者为所有已提交作业的同学或者你们选出的代表。

数词用法归纳

▲掌握小数，分数、百分数和时间、日期的表达法。 【复习要点】 （一）基数词num. 基数词用来表示数目，或者说表示数量的词叫基数词。最基本的基数词如下表所示。 1 one 11 eleven 100 a hundred 2 two 12 twelve 20 twenty 1000 a thousand 3 three 13 thirteen 30 thirty 1，000，000 a million 4 four 14 fourteen 40 forty 10，000，000 ten million 5 five 15 fifteen 50 fifty 100，000，000 a hundred million 6 six 16 sixteen 60 sixty 1，000，000，000 a billion 7 seven 17 seventeen 70 seventy 8 eight 18 eighteen 80 eighty 9 nine 19 nineteen 90 ninety 10 ten 说明： 1．13—19是由个位数加后缀-teen构成。注意其中13、15的拼写是thirteen 和fifteen。 2．20—90由个位数加后缀-ty构成，注意其中20—50的拼写分别是twenty, thirty, forty 和fifty;80的拼写是eighty。 3．其它非整十的两位数21—99是由整十位数加连字符“-”，再加个位数构成。如：81 eighty-one。 4．101—999的基数词先写百位数，后加and再写十位数和个位数。如：691 six hundred and ninety-one。5．1000以上的基数词先写千位数，后写百位数，再加and，最后写十位数和个位数。 如：5893 five thousand eight hundred and ninety-three。在基数词中只有表示“百”、“千”的单位词，没有单独表示“万”、“亿”的单位词，而是用thousand（千）和million（百万）来表达，其换算关系为：1万=10 thousand;1亿=100 million; 10亿=a thousand million=a billion。 Hundreds of Thousands of 6．多位数的读法： 1）1000以上的多位数，要使用计数间隔或逗号“，”。即从个位起，每隔三位加一个间隔或逗号。第一个间隔或逗号前是thousand（千），第二个间隔或逗号前是million（百万），第三个间隔或逗号前是a thousand million或a billion(十亿)。 2）每隔三位分段以后就都成了101—999。读的时候十位数（或个位数）的前面一般要加and。如： 888，000，000读作：eight hundred and eighty-eight million。 基数词的用法： 1. 基数词在句中的作用 基数词的作用相当于名词和形容词，在句中可作定语、主语、宾语（介宾）、表语、同位语等。 例如：Three and five is eight. 3+5=8 （作表语）How many oranges do you want?你要多少桔子？ I want eight. 我要八个。（作宾语）There are eight boats in the lake. 湖里有八条小船。（作定语） 2．Hundred, thousand, million, dozen, score这些词前面如有表示具体数字的词，它们不能加“s”,反之则须加“s”, 并要与of短语连用。例如：

标点符号用法分析

标点符号用法 一、标点符号 标点符号：辅助文字记录语言的符号，是书面语的有机组成部分，用来表示语句的停顿、语气以及标示某些成分（主要是词语）的特定性质和作用。 句子：前后都有较大停顿、带有一定的语气和语调、表达相对完整意义的语言单位。 复句：由两个或多个在意义上有密切关系的分句组成的语言单位，包括简单复句（内部只有一层语义关系）和多重复句（内部包含多层语义关系）。 分句：复句内两个或多个前后有停顿、表达相对完整意义、不带有句末语气和语调、有的前面可添加关联词语的语言单位。 陈述句：用来说明事实的句子。 祈使句：用来要求听话人做某件事情的句子。 疑问句：用来提出问题的句子。 感叹句：用来抒发某种强烈感情的句子。 词语：词和短语（词组）。词，即最小的能独立运用的语言单位。短语，即由两个或两个以上的词按一定的语法规则组成的表达一定意义的语言单位，也叫词组。 二、分类 标点符号分为点号和标号两大类。

点号的作用是点断，主要表示说话时的停顿和语气。点号又分为句末点号和句内点号。 句末点号用在句末，表示句末停顿和句子的语气，包括句号、问号、叹号。 句内点号用在句内，表示句内各种不同性质的停顿，有逗号、顿号、分号、冒号。 标号的作用是标明，主要标示某些成分（主要是词语）的特定性质和作用。包括引号、括号、破折号、省略号、着重号、连接号、间隔号、书名号、专名号、分隔号。 （一）句号 1.用于句子末尾，表示陈述语气。使用句号主要根据语段前后有较大停顿、带有陈述语气和语调，并不取决于句子的长短。 2.有时也可表示较缓和的祈使语气和感叹语气。 请您稍等一下。 我不由地感到，这些普通劳动者也是同样值得尊敬的。 （二）问号 主要表示句子的疑问语气。形式是“？”。 1.用于句子末尾，表示疑问语气（包括反问、设问等疑问类型）。使用问号主要根据语段前后有较大停顿、带有疑问语气和语调，并不取决于句子的长短。 2.选择问句中，通常只在最后一个选项的末尾用问号，各个选项之间一般用逗号隔开。当选项较短且选项之间几乎没有停顿时，选项之间可不用逗号。当选项较多或较长，或有意突出每个选项的独立性时，也可每个选项之后都用问号。 3.问号也有标号的用法，即用于句内，表示存疑或不详。 马致远（1250？―1321）。 使用问号应以句子表示疑问语气为依据，而并不根据句子中包含有疑问词。当含有疑问词的语段充当某种句子成分，而句子并不表示疑问语气时，句末不用问号。

定语从句用法分析

定语从句用法分析 定语从句在整个句子中担任定语，修饰一个名词或代词，被修饰的名词或代词叫先行词。定语从句通常出现在先行词之后，由关系词（关系代词或关系副词）引出。 eg. The boys who are planting trees on the hill are middle school students 先行词定语从句 #1 关系词： 关系代词：who, whom, whose, that, which, as (句子中缺主要成份:主语、宾语、定语、表语、同位语、补语)， 关系副词：when, where, why （句子中缺次要成份：状语）。 #2 关系代词引导的定语从句 关系代词引导定语从句，代替先行词，并在句中充当主语、宾语、定语等主要成分。 1）who, whom, that 指代人，在从句中作主语、宾语。 eg. Is he the man who/that wants to see you?（who/that在从句中作主语） ^ He is the man who/whom/ that I saw yesterday.（who/whom/that在从句中作宾语） ^ 2）whose 用来指人或物，（只用作定语, 若指物，它还可以同of which互换）。eg. They rushed over to help the man whose car had broken down. Please pass me the book whose cover is green. = the cover of which/of which the cover is green. 3）which, that指代物，在从句中可作主语、宾语。 eg. The package （which / that）you are carrying is about to come unwrapped. ^ （which / that在从句中作宾语,可省略） 关系代词在定语从句中作主语时，从句谓语动词的人称和数要和先行词保持一致。 eg. Is he the man who want s to see you? #3.关系副词引导的定语从句 关系副词when, where, why引导定语从句，代替先行词（时间、地点或理由），并在从句中作状语。 eg. Two years ago, I was taken to the village where I was born. Do you know the day when they arrived? The reason why he refused is that he was too busy. 注意： 1）关系副词常常和"介词+ which"结构互换 eg. There are occasions when （on which）one must yield (屈服). Beijing is the place where（in which）I was born. Is this the reason why （for which）he refused our offer? * 2）在非正式文体中，that代替关系副词或"介词+ which"，放在时间、地点、理由的名词，在口语中that常被省略。 eg. His father died the year （that / when / in which）he was born. He is unlikely to find the place （that / where / in which）he lived forty years ago.

pretend的用法总结

pretend的用法总结 以下是小编为大家总结的pretend的用法，希望能帮助大家掌握pretend这个单词，提高英语水平。 pretend to be doing 是强调不定式的动作正在进行的过程中. pretend to do是强调假装要做某事,而不一定正在进行或者是已经发生. 还有一种完成式pretend to have done 强调假装后面的动作已经完成. pretend to be reading就表示他假装正在读书 pretend to sleep 表示他要去睡觉 pretend vt. 假装, 装扮, (作为藉口或理由)伪称 To give a false appearance of; feign: 伪装：显示一副假面貌;伪装： You had to pretend conformity while privately pursuing high and dangerous nonconformism(Anthony Burgess) 当你私下里追求崇高而又危险的新教教义时，你仍得假装信奉国教(安东尼伯吉斯) To claim or allege insincerely or falsely; profess: 假称：不诚实地或虚假地要求或宣称;自称：

doesnt pretend to be an expert. 不要伪称是个专家 To represent fictitiously in play; make believe: 装扮：在戏剧中虚构地扮演;使相信： pretended they were on a cruise. 他们假装在海上巡逻 I cannot pretend to say that you are wrong. 我不敢说你是错误的To take upon oneself; venture: 大胆冒昧地做：使自己承担义务;冒险干某事： v.intr.(不及物动词) To feign an action or a character, as in play. 扮演：假扮某种行为或某个角色，如在戏剧中假扮 To put forward a claim. 自称：提出要求 To make pretensions: 假装，矫作： pretends to gourmet tastes. 自命有美食家的品味 https://www.doczj.com/doc/3111539753.html,rmal (形容词)【非正式用语】 Imitation; make-believe: 模仿的;仿制的： pretend money; pretend pearls.

comparison的用法解析大全

comparison的用法解析大全 comparison的意思是比较，比喻，下面我把它的相关知识点整理给大家，希望你们会喜欢！ 释义 comparison n. 比较;对照;比喻;比较关系 [ 复数 comparisons ] 词组短语 comparison with 与…相比 in comparison adj. 相比之下;与……比较 in comparison with 与…比较，同…比较起来 by comparison 相比之下，比较起来 comparison method 比较法 make a comparison 进行比较 comparison test 比较检验 comparison theorem 比较定理 beyond comparison adv. 无以伦比 comparison table 对照表 comparison shopping 比较购物;采购条件的比较调查 paired comp arison 成对比较 同根词 词根： comparing adj. comparative 比较的;相当的 comparable 可比较的;比得上的 adv. comparatively 比较地;相当地 comparably 同等地;可比较地 n.

comparative 比较级;对手 comparing 比较 comparability 相似性;可比较性 v. comparing 比较;对照(compare的ing形式) 双语例句 He liked the comparison. 他喜欢这个比喻。 There is no comparison between the two. 二者不能相比。 Your conclusion is wrong in comparison with their conclusion. 你们的结论与他们的相比是错误的。 comparison的用法解析大全相关文章： 1.by的用法总结大全

several many 与hundred组合用法

我对hundred, thousand和million三词用法的困惑 我们先看看几道中考试题： 1. Many ______ trees should be planted on the mountains. （2007年山东青岛） A.thousand B.thousand of C. thousands D.thousands of 答案：D 2. In our school several ______ students are able to search the Internet for useful information now. (2003年江苏盐城) A. hundred of B. hundreds for C. hundred D.hundreds 答案：C 3. Beijing is a beautiful city. And ______ foreigh friends come to visit Beijing every month. (2010年贵州铜仁中考样卷) A.many thousand of B. several thousands C. two thousands D.thousands of 答案：D 大家知道，中考在考查学生数词的用法时，hundred, thousand和million三词用法是考查热点。我们都知道当它们前面有具体的数词修饰时，hundred, thousand和million不能加-s, 当它们后面接of时，它们必须加-s. 不管哪种情况，它们都是直接接名词，名词前不能有限定词。 但是，如果hundred, thousand和million前面有many和several等不确定的数修饰时，该如何表达呢？通过上面三题的参考答案，我们可以得出这么一个结论：many是个概数，可以组成many(hundreds, thousands, millions)of +名词复数；several相当于一个具体的数字，组成several((hundred, thousand, million)+名词复数。 然而，笔者查阅了大量资料，似乎又不是这样。关于它们的用法，有的甚至截然相反。 第一种说法：（《牛津高级英汉词典》）P864 hundred的用法之一：“说a, one, two,several,etc.hundred时，hundred后面不加-s; 若前面没有数目或数量，可用hundreds(of…)。Hundred或hundreds均用复数动词”。 这里它把several看成了具体数词。上面第二题选C可能就是这么来的。 第二种说法：（《英语基础词汇用法详解词典》）P836 “下面两个短语都有‘几百人’的意思：several hundred of people; several hundreds of people”。 照这种说法，上面第二题似乎应该选A才对。 第三种说法：（《大学英语语法讲座与测试》）P42 Note: ①当hundred of,thousand of,million of被a few,some,several,many等表示不确定的数的词修饰时，用单数形式或复数形式均可。例如： Several hundred(s) of workers attended the meeting. Some thousand(s) of soldiers were sent there. Many million(s) of birds fly to the south in winter. ②比较下面两句： She earned several hundred(thousand).(用单数) She earned some(many) hundreds(thousands).（用复数） 照这种说法，上面第一题B,D都对；第二题A,C都对；第三题A,B,D都对。