单选题 16. Cotton grass, which grows only in arctic regions, has been the only summertime source of protein available to the caribou. The caribou that do not get adequate amounts of protein in the summer are unable to reproduce the following year. Rising average temperatures in arctic regions, however, are causing cotton grass to disappear. Therefore, if the warming trend continues, the caribou is likely to become extinct.
Which of the following is an assumption on which the argument depends? ______

A、 cotton grass is the only one of the caribou's food source that is becoming scarce as temperatures rise in arctic regions.
B、 caribou that do not eat enough protein to reproduce do not live as long as caribou that do
C、 The warming trend in arctic regions will not enable other plants capable of providing protein to caribou to grow there.
D、 The caribou is the only animal that depends on cotton grass as a major source of food.
E、 If the warming trend continues and cotton grass disappears from arctic regions, then cotton grass will be extinct.

【正确答案】 C

【答案解析】 C：选项取反。温暖趋势会使其他植物为驯鹿提供蛋白质→驯鹿可以获取蛋白质→不会灭绝，削弱原文，正确。注意，有些考生认为该选项重复原文第一句，但是本文第一句的时态是现在完成时，指的是从过去一直到目前，棉花草都是唯一的蛋白质来源。但是该选项的时态是将来时，因此不是重复原文。
A：选项取反。棉花草不是唯一一种会变少的驯鹿食物来源→驯鹿的食物来源变得更稀缺→驯鹿更加无法繁殖→驯鹿灭绝，加强原文，不选。
B：本文讨论的是驯鹿灭绝的前提假设，而该选项讲的是驯鹿会活多久，无关选项，不选。
D：选项取反。驯鹿不是唯一一种将棉花草当作主要食物来源的动物，依然在说驯鹿会依赖于棉花草，再加上原文中提到的棉花草会减少，驯鹿依然有灭绝的可能，加强原文，不选。
E：该选项重复原文，不选。