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In Australia, in years with below-average rainfall, less water goes into rivers and more water is extracted from rivers for drin

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问题 In Australia, in years with below-average rainfall, less water goes into rivers and more water is extracted from rivers for drinking and irrigation. Consequently, in such years, water levels drop considerably and the rivers flow more slowly. Because algae grow better the more slowly the water in which they are growing moves, such years are generally beneficial to populations of algae. But, by contrast, populations of algae drop in periods of extreme drought.
Which of the following, if true, does most to explain the contrast?
选项 A、Algae grow better in ponds and lakes than in rivers.
B、The more slowly water moves, the more conducive its temperature is to the growth of algae.
C、Algae cannot survive in the absence of water.
D、Algae must be filtered out of water before it can be used for drinking.
E、The larger the population of algae in a body of water, the less sunlight reaches below the surface of the water.
答案C
解析 Argument Construction
Situation The quantity of water in Australian rivers greatly diminishes in years of below-average rainfall, When river levels become very low, the rivers flow more slowly. The low flow favors rapid algae growth. However, in periods of extreme drought, algae populations drop.
Reasoning What information would most help to explain the two contrasting trends in algae growth? The. information given indicates that algae proliferate when rivers flow slowly. When the water levels become extremely low, algae populations decrease. In periods of extreme drought, presumably some rivers retain little or no water.
A This has no obvious relevance to explaining the contrast in the algae growth trends.
B Nothing in the given information is explicit about the effects of water temperature and how that changes in rivers with changes in rainfall rates.
C Correct. This information could help explain the decrease in algae populations during periods of extreme drought. It seems quite probable that during such periods, at least parts of some riverbeds would dry out.
D This information does not help explain the contrasting trends in algae growth. Algae filtered out of river water to be used for drinking might not be returned to rivers, and this conceivably could affect algae populations. But it seems likely, based on the given information, that this would occur mainly during low-rainfall non-drought periods, when proliferation of algae has increased, so the impact on algae populations would probably be minimal.
E This information is clearly irrelevant to the contrast that needs to be explained.
The correct answer is C.
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