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.
ans: Australian rivers dry up completely for short intervals in periods of extreme drought.
myuring periods of extreme drought, the populations of some of the species that feed on algae tend to fall.
求问我的选项错在哪儿了？
谢谢！作者: winnielxx 时间: 2013-2-1 21:47
feed on sth是以sth为食，所以the population of some species that feed on algae tend to fall会使algae的数量上升
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uring periods of extreme drought, the populations of some of the species that feed on algae tend to fall.