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雅思g类阅读模拟题READING PASSAGE 2You should spend about 20 minutes on Questions 15-26 which are based on Reading Passage 2 below.An examination of the functioning of the senses in cetaceans, the group of mammals comprising whales, dolphins and porpoises鲸鱼的感官鲸目动物(包括鲸、海豚、鼠海豚等晡乳动物)的感官功能测试。
Some of the senses that we and other terrestrial mammals take for granted are either reduced or absent in cetaceans or fail to function well in water. For example, it appears from their brain structure thattoothed species are unable to smell. Baleen species, on the other hand, appear to have some related brain structures but it is not known whether these are functional. It has been speculated that, as the blowholes evolved and migrated to the top of the head, theneural pathways serving sense of smell may have been nearly all sacrificed. Similarly, although at least some cetaceans have taste buds, the nerves serving these have degenerated or arerudimentary.对我们人类以及其他的陆地哺乳动物来说，有些感官是与生俱来的，然而对于鲸鱼来讲，这些功能要么已经衰退或彻底消失，要么就无法在水中正常发挥作用。
比如说从齿鲸的大脑结构来看，它们是嗅不到气味的;而须鲸虽然有与嗅觉相关的脑部结构，可是我们却无法判断这些结构是否起作用。
据推测，由于鲸鱼的气孔进化并最终移到了头部的正中，所以掌管嗅觉的神经纤维几乎全部不见了。
同样，尽管有些鲸鱼也有味蕾，但这些味觉器官要么已经退化，要么就根本没有发育。
The sense of touch has sometimes been described as weak too, but this view is probably mistaken. Trainers of captive dolphins and small whales often remark on their animals’ responsiveness to being touched or rubbed, and both captive and freeranging cetaceanindividuals of all species (particularly adults and calves, or members of the same subgroup) appear to make frequent contact. This contact may help to maintain order within a group, and stroking or touching are part of the courtship ritual in most species. The area around the blowhole is also particularly sensitive and captiveanimals often object strongly to being touched there.有人认为鲸鱼的触觉也不发达，不过这个观点很可能是错误的。
训练人工饲养海豚和小鲸鱼的人常常会评论他们的小动物对于触碰和抚摩的敏感度。
而无论是人工饲养还是放养，几乎所有种类的鲸鱼个体之间都会进行频繁的接触，特别是在成年鲸鱼和幼鲸之间或同一亚群的成员之间。
这种接触有助于维护同一种群内部的秩序，而且对大多数鲸鱼而言，抚摸和触碰也是求偶仪式的一部分。
气孔周围的部分尤其敏感，一旦被触碰，人工饲养的鲸鱼就会有激烈的反应。
The sense of vision is developed to different degrees in different species. Baleen species studied at close quarters underwater – specifically a grey whale calf in captivity for a year, and free-ranging right whales and humpback whales studied and filmed off Argentina and Hawaii – have obviously tracked objects with vision underwater, and they can apparently see moderately well both in water and in air. However, the position of the eyes so restricts the field of vision inbaleen whales that they probably do not have stereoscopic vision.不同种类的鲸鱼，视觉发达程度也各不相同。
通过研究一只被人工饲养了一年的小灰鲸，以及通过对阿根廷和夏威夷沿海所放养的露脊鲸和座头鲸的研究及拍摄，人们发现在封闭水域中的须鲸显然可以利用视觉来追踪水下的物体，而且它们无论在水中或空气中视力都相当好。
但是眼睛的位置如此严重地限制了须鲸的视野，以致于它们可能不具备立体视觉。
On the other hand, the position of the eyes in most dolphins and porpoises suggests that they have stereoscopic vision forward and downward. Eye position in freshwater dolphins, which often swim on their side or upside down while feeding, suggests that what vision they have is stereoscopic forward and upward. By compare-son, thebottlenose dolphin has extremely keen vision in water. Judging from the way it watches and tracks airborne flying fish, it can apparently see fairly well through the air–water interface as well.And although preliminary experimental evidence suggests that their in-air vision is poor, the accuracy with which dolphins leap high to take small fish out of a trainer’s hand provides anecdotal evidence to the c ontrary.从另一方面来看，大多数海豚和江豚眼睛的位置表明它们是拥有向前及向下的立体视觉的。
淡水海豚经常侧游，或是在吃东西的时候肚皮朝上游泳，这就表明眼睛的位置使它们拥有向前及向上的立体视觉。
相反的是，宽吻海豚在水中视力就很敏锐，而从它观察及追踪空中飞鱼的方式来看，它在水天交界面的视力也相当好。
尽管之前的实验证据表明，海豚在露天环境中可能是睁眼瞎，然而，它们能够从水中跃起很髙，并且能够准确地吃到训练员手中的小鱼，这就有趣地证明了上述观点是错误的。
Such variation can no doubt be explained with reference to the habitats in which individual species have developed. For example, vision is obviously more useful to species inhabiting clear open waters than to those living in turbid rivers and flooded plains. The South American boutu and Chinese beiji, for instance,appear to have very limited vision, and the Indian susus are blind, their eyes reduced to slits that probably allow them to sense only the direction and intensity of light.当然，这些变异可以通过这些品种所生长的环境来解释。
比如说，对于宽广清澈水域中的鲸鱼来说，视觉显然就有用的多;而对于那些住在混浊的河流或水淹的平原上的品种来说，视力显然就没什么大用。
比如，南美洲亚马逊河中的江豚以及中国的白鳍啄视力都相当有限，而印度河中的江豚根本看不见东西，它们的眼睛已经退化成了两条窄缝，除了感知一下方向和光的强度几乎没什么作用。
Although the senses of taste and smell appear to have deteriorated, and vision in water appears to be uncertain, such weaknesses are more than compensated for by cetaceans’ well-developed acousticsense. Most species are highly vocal, although they vary in the range of sounds they produce, and many forage for food using echo-location_ Large baleen whales primarily use the lower frequencies and are often limited in their repertoire. Notable exceptions are the nearly song-like choruses of bowhead whales in summer and the complex, haunting utterances of the humpback whales. Toothedspecies in general employ more of the frequency spectrum, and produce a wider variety of sounds, than baleen species (though the sperm whale apparently produces a monotonous series of high-energy clicks and little else). Some of the more complicated sounds are clearly communicative, although what role they may play in the social life and ‘culture’ of cetaceans has been more the subject of wild speculation than of solid science.尽管鲸鱼们的味觉和嗅觉严重衰退，在水中的视觉又不那么确定，然而这些缺陷完全可以被它们那高度发迖的听觉系统所弥补。
