2017-2018学年高一英语北师大版必修三习题：Unit 8 课下能力提升(七) Word版含答案

课下能力提升(八) 正切函数的定义 正切函数的图像与性质一、选择题1．已知θ是第二象限角，则( ) A ．tan θ2＞0 B ．tan θ2＜0C ．tan θ2≤0D ．tan θ2的符号不确定2．函数y ＝2tan ⎝⎛⎭⎪⎫2x －π4的定义域是( )A.⎩⎨⎧⎭⎬⎫x |x ∈R 且x ≠k π－π4，k ∈ZB.⎩⎨⎧⎭⎬⎫x |x ∈R 且x ≠k π2＋3π8，k ∈Z C.⎩⎨⎧⎭⎬⎫x |x ∈R 且x ≠k π＋3π4，k ∈ZD.⎩⎨⎧⎭⎬⎫x |x ∈R 且x ≠k π2＋π8，k ∈Z 3．函数y ＝tan(sin x )的值域是( ) A.⎣⎢⎡⎦⎥⎤－π4，π4 B.⎣⎢⎡⎦⎥⎤－22，22C ．[－tan 1，tan 1]D ．[－1，1] 4．函数f (x )＝sin x|cos x |在区间[－π，π]内的大致图像是下列图中的( )二、填空题5．若tan x ≥－3，则x 的取值范围是________． 6．函数y ＝lg(tan x )的单调增区间是________．7．函数y ＝sin x 与y ＝tan x 的图像在⎝ ⎛⎭⎪⎫－π2，π2上交点个数是________． 8．已知函数y ＝2tan ⎝ ⎛⎭⎪⎫π6－12x ，则函数的对称中心是________． 三、解答题9．已知f (x )＝a sin x ＋b tan x ＋1，f ⎝ ⎛⎭⎪⎫－2π5＝7，求f ⎝ ⎛⎭⎪⎫2 012π5.10．已知函数f (x )＝x 2＋2x tan θ－1，x ∈[－1， 3 ]，其中θ∈⎝ ⎛⎭⎪⎫－π2，π2.(1)当θ＝－π6时，求函数f (x )的最大值与最小值；(2)求θ的取值范围，使y ＝f (x )在区间[－1， 3 ]上是单调函数．答案1．解析：选A ∵θ是第二象限角， ∴θ2是第一或第三象限角， ∴tan θ2＞0.2．解析：选B 由2x －π4≠k π＋π2，k ∈Z ，解得x ≠k π2＋3π8，k ∈Z . 3．解析：选C ∵－1≤sin x ≤1， ∴－π2<－1≤sin x ≤1<π2.∵y ＝tan x 在(－π2，π2)上是增加的．∴y ∈[－tan 1，tan 1]． 4．解析：选C f (x )＝sin x|cos x |＝⎩⎪⎨⎪⎧tan x ，cos x >0－tan x ，cos x <0 ＝⎩⎪⎨⎪⎧tan x ，－π2<x <π2，－tan x ，－π≤x <－π2或π2<x ≤π.5．解析：作出y ＝tan x ，x ∈⎝ ⎛⎭⎪⎫－π2，π2的图像，如图所示． 令y ＝－3，得x ＝－π3，∴在(－π2，π2)中满足不等式tan x ≥－3的x 的取值范围为⎣⎢⎡⎭⎪⎫－π3，π2. 由正切函数周期性，可知：原不等式的解集为⎣⎢⎡⎭⎪⎫k π－π3，k π＋π2(k ∈Z )．答案：⎣⎢⎡⎭⎪⎫k π－π3，k π＋π2(k ∈Z )6．解析：函数y ＝lg(tan x )有意义，则tan x >0， ∴函数的增区间为(k π，k π＋π2)(k ∈Z )．答案：⎝⎛⎭⎪⎫k π，k π＋π2(k ∈Z ) 7．解析：在x ∈⎝ ⎛⎭⎪⎫0，π2时，tan x >sin x ，x ∈⎝ ⎛⎭⎪⎫－π2，0时，tan x <sin x ，所以y ＝sin x 与y ＝tan x 在⎝ ⎛⎭⎪⎫－π2，π2上只有一个交点(0，0)．答案：18．解析：y ＝2tan ⎝ ⎛⎭⎪⎫π6－12x ＝－2tan ⎝ ⎛⎭⎪⎫12x －π6.∵y ＝tan x 的对称中心为⎝⎛⎭⎪⎫k π2，0，∴令12x －π6＝k π2，得x ＝k π＋π3，k ∈Z .∴y ＝2tan ⎝ ⎛⎭⎪⎫π6－12x 的对称中心为⎝ ⎛⎭⎪⎫k π＋π3，0，k ∈Z .答案：⎝ ⎛⎭⎪⎫k π＋π3，0(k ∈Z )9．解：设g (x )＝a sin x ＋b tan x ，因为sin x 与tan x 都是奇函数，所以g (－x )＝－g (x )，即g (－x )＋g (x )＝0，故f (－x )＋f (x )＝g (－x )＋1＋g (x )＋1＝2，又易得f ⎝⎛⎭⎪⎫2 012π5＝f ⎝⎛⎭⎪⎫402π＋2π5＝f ⎝ ⎛⎭⎪⎫2π5，∵f ⎝ ⎛⎭⎪⎫2π5＋f ⎝ ⎛⎭⎪⎫－2π5＝2，且f ⎝ ⎛⎭⎪⎫－2π5＝7， ∴f ⎝⎛⎭⎪⎫2 012π5＝f ⎝ ⎛⎭⎪⎫2π5＝－5.10．解：(1)当θ＝－π6时，f (x )＝x 2－233x －1＝⎝⎛⎭⎪⎫x －332－43，x ∈[－1， 3 ]．∴当x ＝33时，f (x )的最小值为－43； 当x ＝－1时，f (x )的最大值为233.(2)函数f (x )＝(x ＋tan θ)2－1－tan 2θ的图像的对称轴为x ＝－tan θ. ∵y ＝f (x )在区间[－1，3]上是单调函数， ∴－tan θ≤－1或－tan θ≥3， 即tan θ≥1或tan θ≤－ 3.又θ∈⎝ ⎛⎭⎪⎫－π2，π2， ∴θ的取值范围是⎝ ⎛⎦⎥⎤－π2，－π3∪⎣⎢⎡⎭⎪⎫π4，π2 .。

2017-2018学年北师大版高中英语必修3全册课下能力提升训练Unit 7 课下能力提升(一)Ⅰ.单词拼写1．We have p________ him to accept our ideas.2．You've been in prison six times ________ (根据) to our records.3．They a________for the late departure of this flight.4．She hopes to get a job on the local newspaper and ________ (最终) works for The Times.5．Many experts think the common ________ (祖先) lived at least seven million years ago.6．The v________ took months and first brought him to Moscow, then westward.7．She was a very brave girl and everyone who knew her admired her ________ (精神)．8．All CEOs love a good well­prepared 90­minute l________．Ⅱ.完成句子1．不久你就会意识到是你错了。

It will not be ________________ you ________ you are wrong.2．他为让我们等待数小时而向我们道歉。

He __________________ having kept us waiting for hours.3．有很多乘客正在公共汽车站等车。

There were many passengers ________________ the bus at the bus stop.4．我们不得不求助于老师，因为只有老师才能说服他不再上网。

Unit 8 课下能力提升(八)Ⅰ.单词拼写1．Britain built up her wealth by t________ with other countries.2．I'll help as mush as I can, but there is a l________ to what I can do.3．Have you o________ anything strange in her words?4．The school ________ (全体员工) gathered to have the meeting.5．He was ________ (影响) by his teacher to take up the study of medicine.Ⅱ.完成句子1．我认为这项研究十分重要。

I ________________ this research.2．她喜欢水果，尤其是苹果。

She likes fruit, __________________________________________.3．我们来到一个小茅屋，在那里避了雨。

We reached a little hut, where we ________________________________________．4．这片地域就是中国最大的恐龙公园的归属地。

The site ________________ China's largest dinosaur park.5．返巢本能通常是与动物世界联系在一起的。

The homing instinct is usually _______________________________________.Ⅲ.翻译句子1．Associated with the scandal, the superstar lost his fans' support.________________________________________________________________________2．由于种种原因，我们未能约定聚会日期。

Unit 9 课下能力提升(十二)Ⅰ.单词拼写1．The children were a________ over which TV program to watch.2.He must have reached his l________ of patience, for he lost his temper.3．C________ with most of your classmates, you are lucky.4．The d________ the storm caused was beyond repair.5．We should make a good ________ (关系) with neighbours.6．I can't ________ (负担) a holiday this summer.7．Finding a date that ________ (适合) us all is very difficult.8．Twice, I was ________ (联系) to the wrong person, so I had to dial a third time.Ⅱ.词义辨析1．damage/destroy(1)A fire ________ the house.(2)Smoking seriously ________ your health.2．charge/fee/tip/fare(1)When you take a bus you have to pay the ________．(2)Is this money enough for the tuition ________？(3)The guidebook to the museum is available free of ________．(4)I gave the barber a ________．Ⅲ.选词填空be worried about, so far, take part in, because of, complain about, succeed in, havea bad impression of, keep in touch with, take place1.After three year's hard work, he ________________ passing the University Entrance Examination.2．He is a naughty and lazy student, so his teachers ________________ him.3．This is the best film I have seen ________________．4．We still ________________ each other after we graduated from university.5．Our school opening ceremony is to ________________ on the playground next week.6．He can't ________________ the competition ____________________ his illness.7．It seems that many people always ________________ their work.8．With a lot of exercises undone, he ________________ the coming exam.Ⅳ.完成句子1．The rainstorm ________________ (对……造成巨大破坏) the old buildings.2．Though the students have graduated, they ________________ (经常来看我)．3．The fares ________________ (一直在上升) because the price of petrol keeps going up.4．There was nothing _____________ him ____________ (把……与……联系起来) the crime.5．Getting up at 5：00 am ________________ (很适合我)．6．A guess ____________________ facts (以事实为依据的) is called a theory.7．There are 400 visitors to the park ____________ (平均起来) every week.Ⅴ.完形填空The first day of school our professor asked us to know someone we didn't know. I turned___1__ to find a little lady smiling at me.She said, “Hi handsome. I'm Rose, eighty ­seven years old.Can I give you a __2__？”I laughed and responded, “Of course you __3__！” and she gave me a big squeeze.“Why are you in college at such an innocent (无辜的) __4__？” I asked.She__5__ replied, “To meet a __6__ husband, get married, and have a couple of kids ...”“No seriously，” I asked.“I always __7__having a college education and now I'm getting one！” she told me.After class we talked a lot and became instant friends. Every day for the next three months we would__8__ class together and then talk nonstop. Actually, she easily __9__ friends wherever she went.__10__ the end of the semester we __11__ Rose to speak at our football banquet (宴会)．I'll never forget what she __12__ us. As she began to __13__her speech, she __14__ her cards on the floor. As we laughed she __15__ her throat (喉咙) and began, “We do not stop playing because we are old; we grow old __16__ we stop playing. There are four __17__ to staying young, being happy, and achieving success. You have to laugh and find __18__ every day. You have to have a dream. When you__19__ your dreams, you die.”She ended her __20__ by courageously singing The Rose.1．A.round B．onC．off D．away2．A.gift B．hugC．kiss D．dream3．A.must B．may。

2017-2018学年高一英语(北师大版) 必修三全册教学案Killer whales have the second­heaviest brains among marine mammals (after Sperm whales, which have the largest brain of any animal). They can be trained in captivity (囚禁；关押) and are often described as intelligent, although defining and measuring “intelligence” is difficult in a species whose environment and behavioral strategies are very different from those of humans.Killer whales imitate others, and seem to deliberately teach skills to their kin. Off the Crozet Islands, mothers push their calves onto the beach, waiting to pull the youngster back if needed.People who have interacted closely with killer whales offer numerous anecdotes demonstrating (证明) the whales' curiosity, playfulness, and ability to solve problems. Alaskan killer whales have not only learned how to steal fish from Iong lines, but also have overcome avariety of techniques designed to stop them, such as the use of unrated (未分级的；未征税的) lines as decoys. Once, fishermen placed their boats several miles apart, taking turns retrieving (恢复；取回) small amounts of their catch, in the hope that the whales would not have enough time to move between boats to steal the catch as it was being retrieved. A researcher described what happened next: The killer whale's use of dialects and the passing of other learned behaviours from generation to generation have been described as a form of animal culture.Section_ⅠWarm­up__&_Lesson_1_—_Pre­reading[原文呈现]VIKING VOYAGES①TO AMERICAThe Vikings②were the first Europeans to reach America③. They achieved④this long before⑤Columbus ever set sail⑥.The Vikings were a group of people whose ancestors⑦came from Scandinavia⑧. They controlled the seas and coasts of Northern Europe between the 8th and 10th centuries AD⑨. By around 900 AD, there were many places in Northern Europe where the Vikings chose to live⑩. In 982 AD, when a man called Eric the Red⑪decided to set sail further⑫west, there were as many as 10,000 Vikings living in Iceland ⑬.[读文清障]①voyage/'vɔIIdʒ/n．航海；航空②Viking/'vaIkIŋ/n．维京人，北欧海盗③名词中心词被序数词或the last 等修饰时，其后通常用动词不定式作后置定语。

Unit8 Green livingSection ⅠTopic Talk & Lesson 1 .................................................................................. - 1 -Section ⅡLesson 2 & Lesson 3 ................................................................................... - 7 -Section ⅢReading & Writing .................................................................................... - 11 -单元综合测验................................................................................................................ - 17 -Section ⅠTopic Talk & Lesson 1Ⅰ.单词拼写根据首字母或汉语提示写出单词1．The test will involve(包含)answering questions about a photograph.2．We will then have a firmer foundation(基础)of fact on which to build theories.3．Our institute(研究院)has ordered a great many instruments from the company.4．Polluted air and water are harmful to people's health.5．I was bothered about the blister on my hand.6．Why do you think others might have an opposingview?7．The child couldn't keep his balance on his new bicycle.8．We recycle all our empty food and drink cans.9．His movie of the extinction(灭绝)of dinosaurs is a great success.10．Britain's future as a leading industrial(工业的)nation depends on investment.Ⅱ.阅读理解AH ave you ever thought about living in a “green” house，one that is healthy for you and your family and helps conserve the Earth's resources？Some people want to build a new home，renovate an existing one，or make a few changes in their living habits.Every household can do something to support the conservation of the environment and improve our quality of life.As environmental concerns continue to increase worldwide，using more green products into our lives becomes more and more important.There is growing interest in green living，and the possibilities for achieving itin our homes are rapidly expanding.Our company's website can show you more about that.Because buildings need enormous quantities of the Earth's resources in their construction and daily operation，they offer many opportunities for new eco­friendly design as well as cost savings.The Green House shows the combination of architecture，interior­design，and environmental responsibility.Home is where going green begins—where we as individuals have the power to set a new course for a brighter future.If you are interested in these “green”houses，please contact us and our company will send you more information about them.And we're sure you'll have a surprise.E­mail：ghouseabc@Phone：3567218/3567219Fax：33902311．The main purpose of the passage is to ________．A．remind people to protect the environmentB．ask people to buy a “green”houseC．give a brief introduction of the “green”houseD.express the writer's own opinion about the environmentB[推理判断题。

Section_ⅢLesson_2_&_Lesson_3_—_Pre-reading_[原文呈现]Marco Polo and His TravelsMarco Polo was born in Italy in 1254. When he was 17 years old, he travelled across Europe and Asia with his father, who wanted to do trade①with the Chinese②. Eventually③，they arrived in Beijing. At that time, China was ruled by the Yuan Dynasty Emperor④，Kublai Khan.Kublai Khan welcomed Marco and his father. He was very happy to meet two foreigners and wanted to learn all about Europe. Marco and his father were guests at the Emperor's Palace. Although Marco was young, he was very clever and could already speak four languages. The Emperor was impressed⑤by him and they became friends. He asked Marco to serve⑥in his court⑦and sent him to do many important tasks across the country.Marco, in turn⑧，was amazed⑨by how beautiful and powerful China was. He was very impressed by Beijing and the Emperor's Palace, especially⑩the Summer Palace ⑪which he described as⑫“The greatest palace that ever was ... The walls were covered in gold and silver and the Hall was so large it could easily seat⑬6,000 people for dinner⑭.”There were inventions and developments in China which were not available⑮in Europe at that time⑯. Marco was surprised to see Chinese people using paper money in the markets. In Europe, people paid for goods⑰with gold or silver. He could not understand how people could pay for food and valuable things with paper! He was also confused⑱by the black stones people used to burn for fuel⑲. The black stones were coal, but Marco had never seen coal before！[读文清障]①trade v．做买卖n．买卖，交易trade with sb. in sth.同某人做某方面的生意②who引导非限制性定语从句，修饰his father。

Unit 8课下能力提升(六)Ⅰ.单句语法填空1．She very ________ (obvious) wanted to be left alone.2．The captain was not willing to risk ________ (take) his ship through the straits until be could see where he was going.3．He sent off copies to ________ (vary) people for them to read and make comments.4．He knew how important a piece of ________ (equip) the radio was when he could get touch with the outside.5．She tried not to show ________ (prefer) in her treatment of the children in her care.6．Do you know what EEC stands ________？7．If a nuclear war breaks ________，every living thing will be wiped off the face of the earth.8．The shop assistants had to have their days off ________ turns.Ⅱ.选词填空in order to, turn up, back out, get ... across, in turn, break out, stand by, put into prison1．Jack agreed to get here at seven, but it has been seven twenty. He hasn't ____________．2．He explained the problem several times, but still he couldn't ________ it ________ to his students.3．Leonardo da Vinci is said to have bought birds kept in cages ________________ have the pleasure of setting them free.4．I promised to help and I'm not ____________ now.5．He was ________________ two years ago for stealing things and will be set free next year.6．Families living on the same floor share one kitchen, so they have to cook ____________ every day.7．No matter what happens, I will ____________ you and support you forever.8．When the war ____________，the family escaped to Asia.Ⅲ.课文缩写语法填空17-year-old Marco Polo travelled across Europe and Asia with his father, and because his father wanted to do trade 1.________ the Chinese, they 2.________ (eventual) eventually arrived in Beijing during the Yuan Dynasty.Marco was very clever and could speak four languages, 3.________ impressed Emperor Kublai Khan. So the Emperor asked him 4.________ (serve) in the court and do many important tasks. Marco was amazed 5.________ how beautiful and powerful China was and was very impressed by Beijing and the Emperor's palace. He was surprised to see Chinese people using paper money to pay for goods. Marco was also 6.________ (confuse) by theblack stones people used to burn for fuel.After 17 years of service to the Emperor, Marco became 7.________ (wealth) and returned to Italy. He was caught in a local war and put 8.________ prison. But he was 9.________ (luck) enough to meet a prisoner who was an author and interested in his stories about China. The prisoner wrote the stories 10.________ Marco told in a book, which became one of the best-selling books in Europe.Many people didn't believe the stories, but Marco said he had only told half of what he had seen.Ⅳ.阅读理解Some people say, “Extreme sports are so dangerous. Why would anyone want to do them？” But the danger is what makes them so exciting. Keep reading to find out the most popular ones.Bungee jumping: People on some South Pacific islands have been bungee jumping for hundreds of years. In 1979, some people bungee jumped off a bridge in England and made the sport popular around the world. Bungee jumping came to China in 1996.Skateboarding: At first, this sport was called “sidewalk surfing”. Skateboarders often jump high into the air, go down steps or slide (滑行) down rails on their boards. They wear baggy trousers so they can move more freely.Skydiving: This is probably the scariest (最惊险的) extreme sport. Skydivers jump out of airplanes about four kilometers up in the sky. They usually free fall for a while and then open a parachute to slow down for a safe landing.Snowboarding：This became a Winter Olympic sport in 1998. People tied their feet to the board with special shoes. They don't use any ski sticks. Then they ride down hills, jump high and do tricks.1．What made bungee jumping popular all over the world?A．A history of hundreds of years.B．Jumping over a river in America.C．Coming to China in 1996.D．Jumping off a bridge in England.2．In which sport do people jump from a plane or from a high place?A．Bungee jumping and skydiving.B．Skydiving and skateboarding.C．Bungee jumping and skateboarding.D．Snowboarding and skateboarding.3．Why do some people like to do the extreme sports?A．It's easy to learn.B．It's exciting and safe.C．It's scary but safe.D．It's dangerous but exciting.Ⅴ.任务型阅读I live in the country and the water where I live is very rusty (腐蚀的)．Sometimes my toilet looks like it hasn't been cleaned for 40 years. So I have found myself looking for tips on how to keep a toilet clean. 1.________Magic erasers! If you put a chunk (大块) of a magic eraser in the tank of your toilet it will clean every time you flush (用水冲洗). 2.________ I think it's a great idea to throw a used-up magic eraser in there rather than ripping up a new one too.3．________ If you poke a hole into a bottle of vinegar and then put the whole bottle into your toilet tank, the vinegar will help you use less water with every flush!Wet dry sand paper works really well for scrubbing stubborn stains! 4.________，however, as it will scratch the surface.5．________ I think it would be a good idea to make full use of the suggestions above so that it can help you to fight against the stains the whole time you are away.A．This really works!B．A small bottle of vinegar!C．Here is what I have found so far.D．You can use wet dry sand paper whenever you like.E．So there you have some tips for battling against rusty water in a toilet.F．Do not use sand paper on any of your other bathroom surfaces.G．It is necessary to use a new magic eraser.Ⅵ.短文改错During the weekend I traveled by air the first time in my life.I generally travel by train and bus.It is both cheaper and safe.But this was a short journey.In the beginning I did not feel very happily, but this feeling did not last longer.The journey was very exciting.I was soon high up in the sky among the cloud.The views of mountains, fields and rivers were interested.I enjoy my short and comfortable journey very much.This experience has shown that traveling in air is actually the safest way of make journeys.答案：Ⅰ.1.obviously 2.taking 3.various 4.equipment 5.preference 6.for7.out8.byⅡ.1.turned up 2.get; across 3.in order to 4.backing out 5.put into prison 6.in turn 7.stand by 8．broke outⅢ.1.with 2.eventually 3.which 4．to serve 5.by 6.confused7．wealthy8.into9.lucky 10．thatⅣ.语篇解读：本文介绍了几项极限运动，虽然危险但却刺激。

Lesson3Marco Polo课后篇巩固提升一、根据句意及首字母提示补全句子,使句子完整正确1.After the police looked at the picture,he was a to find that the big cat turned out to be a)..No nation,however large or small,w or poor,can escape the impact of climate change..At the age of 12 the boy was already an experienced t,having flown all over the world.To keep the enemy out of his empire,E Qinshihuang had all the walls joined up..There will be tax increases on a wide range of g and services..The more we find out about the universe,the more c we seem to become..He is the a of three books on art..It strikes me that what they lack in q,they make up in quality.1a.I could not help being at his freedom and ease as he laughed and chatted aloud in the train and at the station.a.We were thrown off the track in looking for his house by some directions.b.With long hair and a long gray beard,Saddam Hussein looked and very tired.a.I what I said earlier.b.Do you know what EEC ?a.If a nuclear war ,every living thing will be wiped off the face of the Earth.b.Dad would occasionally with an amusing comment.a.The shop assistants had to have their days off .b.Interest rates were cut and,,share prices rose.,每空一词1.I think viewers a film that allows them to be a character in it.2. you Einstein on a Chinese stamp??.Not only had the poor man been arrested,but heas well.,而且还被送进了监狱。

高考提能练Unit 8 仿真检测灵活拆组卷第一部分听力(满分30分，限时20分钟)第一节(共5小题；每小题1.5分，满分7.5分)听下面5段对话，每段对话后有一个小题，从题中所给的A、B、C三个选项中选出最佳选项，并标在试卷的相应位置。

听完每段对话后，你都有10秒钟的时间来回答有关小题和阅读下一小题。

每段对话仅读一遍。

1．What's the original price of the jacket?A．$120.B．$170.C．$240.2．Where does this conversation take place?A．At a restaurant.B．At an airport.C．At a theater.3．What do they need to buy?A．Beef and tomatoes.B．Onions and potatoes.C．Onions and beef.4．What does the girl suggest the boy do?A．Buy a guitar.B．Find a part-time job.C．Pay more attention to study.5．What will the man do on Saturday evening?A．Go to the cinema.B．Have music lessons.C．Stay at home.第二节(共15小题；每小题1.5分，满分22.5分)听下面5段对话或独白。

每段对话或独白后有几个小题，从题中所给的A、B、C三个选项中选出最佳选项，并标在试卷的相应位置。

听每段对话或独白前，你将有时间阅读各个小题，每小题5秒钟；听完后，各小题将给出5秒钟的作答时间。

每段对话或独白读两遍。

听第6段材料，回答第6、7题。

6．Who is the man most probably?A．A hotel receptionist.B．A taxi driver.C．A tour guide.7．How much tip did the man get?A．3.50 dollars.B．2.50 dollars.C．1.50 dollars.听第7段材料，回答第8、9题。