GMAT考试阅读资料(六)a

Passage 29
　　Studies of the Weddell seal in the laboratory have　described the physiological¹ mechanisms³ that allow the　seal to cope with the extreme oxygen deprivation⁴ that　occurs during its longest dives， which can extend 500（5） meters below the ocean‘s surface and last for over 70　minutes. Recent field studies， however， suggest that during more typical dives in the wild， this seal’s physio-logical behavior is different.
　　In the laboratory， when the seal dives below the（10） surface of the water and stops breathing， its heart beats　 more slowly， requiring less oxygen， and its arteries⁵ become constricted⁶， ensuring that the seal‘s blood　 remains⁷ concentrated near those organs most crucial to its ability to navigate⁸ underwater. The seal essentially（15） shuts off the flow of blood to other organs， which either stop functioning until the seal surfaces or switch to an　 anaerobic⁹ （oxygen-independent） metabolism¹⁰. The latter results in the production of large amounts of lactic¹¹ acidwhich can adversely¹² affect the pH of the seal’s blood（20） but since the anaerobic metabolism occurs only in those tissues which have been isolated¹³ from the seal‘s blood supply， the lactic acid is released into the seal’s blood only after the seal surfaces， when the lungs， liver， and other organs quickly clear the acid from the seal‘s blood-（25） stream.
　　Recent field studies， however， reveal that on dives in　the wild， the seal usually heads directly for its prey¹⁴ and　returns to the surface in less than twenty minutes. The　absence of high levels of lactic acid in the seal‘s blood（30） after such dives suggests that during them， the seal’s　organs do not resort to the anaerobic metabolism　observed in the laboratory， but are supplied with oxygen　from the blood. The seal‘s longer excursions underwater，during which it appears to be either exploring distant（35） routes or evading¹⁵ a predator¹⁶， do evoke¹⁷ the diving　response seen in the laboratory. But why do the seal’s　laboratory dives always evoke this response， regardless　of their length or depth？ Some biologists speculate that　because in laboratory dives the seal is forcibly（40） submerged， it does not know how long it will remain　underwater and so prepares for the worst.

　　1. The passage provides information to support which of　the following generalizations¹⁸？
　　　（A） Observations of animals‘ physiological behavior in the wild are not reliable unless verified by laboratory studies.
　　　（B） It is generally less difficult to observe the physiological behavior of an animal in the wild than in the laboratory.
　　　（C） The level of lactic acid in an animal‘s blood is likelyto be higher when it is searching for prey than whenit s evading predators¹⁹.
　　　（D） The level of lactic acid in an animal‘s blood is likely to be lowest during those periods in which it experiences oxygen deprivation.
　　　（E） The physiological behavior of animals in a laboratory setting is not always consistent with their physiological behavior in the wild.

　　2. It can be inferred from the passage that by describing the　Weddell seal as preparing “for the worst” （line 41）， biologists mean that it
　　　（A） prepares to remain underwater for no longer than twenty minutes
　　　（B） exhibits physiological behavior similar to that which characterizes dives in which it heads directly for its prey
　　　（C） exhibits physiological behavior similar to that which characterizes its longest dives in the wild.
　　　（D） begins to exhibit predatory behavior
　　　（E） clears the lactic acid from its blood before attempting to dive

　　3. The passage suggests that during laboratory dives， the pH of the Weddell seal‘s blood is not adversely affected²⁰ by the　production of lactic acid because
　　　（A） only those organs that are essential to the seal‘s ability to navigate underwater revert²¹ to an anaerobic mechanism².
　　　（B） the seal typically reverts²² to an anaerobic metabolism only at the very end of the dive
　　　（C） organs that revert to an anaerobic metabolism aretemporarily isolated from the seal‘s bloodstream
　　　（D） oxygen continues to be supplied to organs that clear　lactic acid from the seal‘s bloodstream
　　　（E） the seal remains submerged for only short periods of time

　　4. Which of the following best summarizes the main point of the passage？
　　　（A） Recent field studies have indicated that descriptions of the physiological behavior of the Weddell sealduring laboratory dives are not applicable to its mosttypical dives in the wild.
　　　（B） The Weddell seal has developed a number of unique　mechanisms that enable it to remain submerged at depths of up to 500 meters for up to 70 minutes.
　　　（C） The results of recent field studies have made it necessary for biologists to revise previousperceptions of how the Weddell seal behavesphysiologically during its longest dives in the wild.
　　　（D） Biologists speculate that laboratory studies of the physiological behavior of seals during dives lastingmore than twenty minutes would be more accurate ifthe seals were not forcibly submerged.
　　　（E） How the Weddell seal responds to oxygen deprivation during its longest dives appears to depend on whether the seal is searching for prey or avoiding predators during such dives.

　　5. According to the author， which of the following is true　of the laboratory studies mentioned in line 1 ？
　　　（A） They fail to explain how the seal is able to tolerate the increased production of lactic acid by organs that revert to an anaerobic metabolism during its longest dives in the wild.
　　　（B） They present an oversimplified account of mechanisms that the Weddell seal relies on during its longest dives in the wild.
　　　（C） They provide evidence that undermines the view that the Weddell seal relies on an anaerobic metabolism during its most typical dives in the wild.
　　　（D） They are based on the assumption that Weddell seals rarely spend more than twenty minutes underwater　　 on a typical dive in the wild.
　　　（E） They provide an accurate account of the physiological behavior of Weddell seals during those dives in the wild in which they are either  evading predators or exploring distant routes.

　　6. The author cites which of the following as characteristic of the Weddell seal‘s physiological behavior during　 dives observed in the laboratory？
　　　Ⅰ. A decrease in the rate at which the seal‘s heart beats
　　　Ⅱ. A constriction²³ of the seal‘s arteries
　　　Ⅲ. A decrease in the levels of lactic acid in the seal‘s blood　
　　　Ⅳ. A temporary halt in the functioning of certain organs
　　　（A） Ⅰand Ⅲ only
　　　（B） Ⅱ and Ⅳ only
　　　（C） Ⅱ and Ⅲ only
　　　（D） Ⅰ，Ⅱ， and Ⅳ only
　　　（E） Ⅰ，Ⅲ， and Ⅳ only

　　7. The passage suggests that because Weddell seals are　forcibly submerged during laboratory dives， they do which of the following？
　　　（A） Exhibit the physiological responses that are characteristic of dives in the wild that last less than twenty minutes.
　　　（B） Exhibit the physiological responses that are characteristic of the longer dives they undertake in the wild.
　　　（C） Cope with oxygen deprivation less effectively than they do on typical dives in the wild.
　　　（D） Produce smaller amounts of lactic acid than they do on typical dives in the wild.
　　　（E） Navigate less effectively than they do on typical dives in the wild