博智教育 GMAT培训 GMAT每日一题
When there is less rainfall than normal, the water level of Australian rivers falls and the rivers flow more slowly. Because algae whose habitat is river water grow best in slow-moving water, the amount of algae per unit of water generally increases when there has been little rain. By contrast, however, following a period of extreme drought, algae levels are low even
in very slow-moving river water.
Which of the following, if true, does most to explain the contrast described above?
(A) During periods of extreme drought, the populations of some of the species that feed on algae tend to fall.
(B) The more slowly water moves, the more conducive its temperature is to the growth of algae.
(C) When algae populations reach very high levels, conditions within the river can become toxic for some of the other species that normally live there.
(D) Australian rivers dry up completely for short intervals in periods of extreme drought.
(E) Except during periods of extreme drought, algae , levels tend to be higher in rivers in which the flow has been controlled by damming than in rivers that flow freely.
题目分析：问题解释题目在原文中一定会有一个矛盾点:明明少雨河流流速慢海藻长的快，但是为什么有一段干旱的时间反而没有海藻了。A说因为在干旱的时候吃海藻的物种少了，不对啊，如果吃海藻的生物少了，海藻应该多啊，不能解释原文那个现象。B说水流慢，但是温度越利于海藻的增长。那怎么海藻还少了呢？不能回答问题。C说当还早多到一定数量的时候，水环境会对其他物种有毒，对其他物种有毒不会影响海藻本身数量多少，杀。D说在极端干旱的情况下河流完全干了，那海藻就完蛋了，流速慢前提是还有水啊，连水都没了当让活不了，可以回答问题，留着。E说在极端干旱的情况下，海藻在哪种环境下增长速度更快，也没有解释为什么海藻少了，杀。
博智教育 GMAT培训 GMAT每日一题
