求教GWD6-Q11

cindy321

GWD6-Q9 to Q12:

Thesloth bear, an insect-eating animal native to Nepal, exhibits only one behaviorthat is truly distinct from that of other bear species:  the females carry their cubs (at leastpart-time) until the cubs are about nine months old, even though the cubs canwalk on their own at six months. Cub-carrying also occurs among some other myrmecophagous (ant-eating)mammals; therefore, one explanation is that cub-carrying is necessitated bymyrmecophagy, since myrmecophagy entails a low metabolic rate and high energyexpenditure in walking between food patches. However, although polar bears’ locomotion is similarly inefficient, polarbear cubs walk along with their mother. Furthermore, the daily movementsof sloth bears and American black bears which are similar in size to slothbears and have similar-sized home ranges reveal similar travel rates anddistances, suggesting that if black bear cubs are able to (26) keep up with their mother, so too should sloth bear cubs.

      An alternative explanation is defense frompredation.  Black bear cubs use trees fordefense, whereas brown bears and polar bears, which regularly inhabit treelessenvironments, rely on aggression to protect their cubs.  Like brown bears and polar bears (and unlikeother myrmecophagous mammals, which are noted for their passivity), sloth bearsare easily provoked to aggression. Sloth bears also have relatively large canineteeth, which appear to be more functional for fighting than for foraging.  Like brown bears and polar bears, sloth bearsmay have evolved in an environment with few trees.  They are especially attracted to food-rich grasslands;although few grasslands persist today on the Indian subcontinent, this type ofhabitat was once wide spread there. Grasslands support high densities of tigers, which fight and sometimeskill sloth bears; sloth bears also coexist with and have been killed bytree-climbing leopards, (52) and areoften confronted and chased by rhinoceroses and elephants, which can toppletrees (53).Collectively these factors probably selected against tree-climbingas a defensive strategy for sloth bear cubs. Because sloth bears are smaller thanbrown and polar bears and are under greater threat from dangerous animals, theymay have adopted the extra precaution of carrying their cubs.  Although cub-carrying may also be adoptivefor myrmecophagous foraging, the behavior of sloth bear cubs, which climb ontheir mother’s back at the first sign of danger, suggests that predation was akey stimulus.

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GWD6-Q11:

Which ofthe following, if true, would most weaken the author’s argument in lines 18-26(“Furthermore … sloth bear cubs”)?

A.   Cub-carrying behavior has been observed inmany non-myrmecophagous mammals.

B.   Many of the largest myrmecophagous mammalsdo not typically exhibit cub-carrying behavior.

C.   Some sloth bears have home ranges that aresmaller in size than the average home ranges of black bears.

D.   The locomotion of black bears issignificantly more efficient than the locomotion of sloth bears.

E.    The habitat of black bears consists ofterrain that is significantly more varied than that of the habitat of slothbears.

给出的答案是D，不过感觉E更准确啊，因为D说的内容不在所划范围里面，我觉得E选项里的habitat terrain 和原文的home range是相同指代吧~
求大牛指点啊~~

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