GMAT考题：OG2018-CR-648

GMAT考题

题库 / OG2018-CR-648

Between 1980 and 2000 the sea otter population of the Aleutian Islands declined precipitously. There were no signs of disease or malnutrition, so there was probably an increase in the number of otters being eaten by predators. Orcas will eat otters when seals, their normal prey, are unavailable, and the Aleutian Islands seal population declined dramatically in the 1980s. Therefore, orcas were most likely the immediate cause of the otter population decline.

Which of the following, if true, most strengthens the argument?

The population of sea urchins, the main food of sea otters, has increased since the sea otter population declined.

Seals do not eat sea otters, nor do they compete with sea otters for food.

Most of the surviving sea otters live in a bay that is inaccessible to orcas.

The population of orcas in the Aleutian Islands has declined since the 1980s.

An increase in commercial fishing near the Aleutian Islands in the 1980s caused a slight decline in the population of the fish that seals use for food.

考题讲解

毕出

情景：在1980年~2000年水獭的数量下降了。没有疾病或者是营养缺乏的迹象。Orcas在没有海豹的情况下会增多，并且他们也吃水獭。因此，Orcas是水獭数量下降的原因。

推理：推理文段是明显的探求原因型的文段，所以是果因推理。（请注意不是相关因果推理，因为前提中并没有说Orcas确实出现了）
顺序的因果逻辑：因为Orcas是水獭数量下降的原因，所以在1980年~2000年水獭的数量下降了
（果）前提：在1980年~2000年水獭的数量下降了
（因）结论：Orcas是水獭数量下降的原因

选题方式：果因推理有两个评估方向，简而言之，即（由于本题问的是加强，所以答案选项需在“取非”后满足），要么给“Orcas是水獭数量下降的原因”另一个原因，要么给出因果联系问题。

选项分析：

A选项：海胆，一个水獭最主要的食物，在水獭数量下降时上升了。本选项不能解释为什么水獭数量下降。

B选项：海豹既不会吃水獭，也不会和水獭抢食物。本选项讨论的是海豹的性质，和水獭数量的下降无关。

C选项：大部分幸存的水獭生活在一个Orcas不能到达的地方。本选项表示Orcas和水獭的数量之间有联系，即，Orcas吃掉了绝大部分的水獭，剩余的都在Orcas进不去的地方了。属于CQ2：因果联系问题。

D选项：Orcas的数量自从1980s也下降了。Orcas的数量下降并不代表它们不能吃很多水獭。

E选项：上升的商业捕鱼引起了海豹食物数量的下降。本选项和推理文段的因果无关。