og12- cr62

pangpangshin

When there is less rainfall than normal, the water level
of Australian rivers falls and the rivers fl ow 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
fl ow has been controlled by damming than in
rivers that fl ow freely.

答案是D。我选的是A   想不明白啊！  求指教！

sunniers

feed on 以..为食，有没有看错~~
A是说以藻类为食的物种数量下降

吃藻类的动物少了  ，可能藻类数量会上升呢~
这就不能解释 极度干旱后 藻类数量低了

pangpangshin

哦！ 对对  以为是藻类的食物下降了呢。。  感谢

evenlasting

algae levels are low even in very slow-moving river water,还是在water环境中的呀，怎么D选项就说dry up了algae 就没了呢？不懂

danni423

(D) Australian rivers dry up completely for short
intervals in periods of extreme drought.

澳大利亚河流完全干涸，在嫉妒干旱的一个很短的时间段内。
首先用排除法:
A 与结论刚好想法
B 水流动越慢，越有利于海藻生存。-- 无关
C 海藻越多，毒越多，不利于其他物种生存 -- 无关
D 澳大利亚河流完全干涸，在极度干旱的一个很短的时间段内。（海藻生存需要水）有点沾边，先留着
E  无关，前半句就直接排除了。
所以选D. 其他更错了。