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Inthe late 1980s, the population of sea otters in the North Pacific Ocean beganto decline. Of the two plausible explanations for the decline — increasedpredation by killer whales or disease — disease is the more likely. After all, aconcurrent sharp decline in the populations of seals and sea lions was almostcertainly caused by a pollution-related disease, which could have spread to seaotters, whereas the population of killer whales did not change noticeably. Whichof the following, if true, most seriously weakens the reasoning? A. Killer whales in the North Pacific usually prey onseals and sea lions but wil, when this food source is scarce, seek out otherprey. B. There is no indication thatsubstantial numbers of sea otters migrated to other locations from the NorthPacific in the 1980s. C. Along the Pacific coast ofNorth America in the 19805, sea otters were absent from many locations wherethey had been relatively common in former times. D. Following the in the populationof the sea otters, there was an increase in the population of sea urchins,which are sea otters ’ main food source. E. The North Pacific populationsof seals and sea lions cover a wider geographic area than does the populationof sea otters.
是这个吗 |
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