2. 考研
  3. Acid rain leads to fish mortality.Many species of fish cannot survive in aquatic environments where the pH is below 5.0.If the w

Acid rain leads to fish mortality.Many species of fish cannot survive in aquatic environments where the pH is below 5.0.If the w

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问题     Acid rain leads to fish mortality.Many species of fish cannot survive in aquatic environments where the pH is below 5.0.If the water is too acid, the gill systems of many kinds of fish can be damaged.【C1】______, the acid alters the blood chemistry of all fish.As a result, the fish population in an acidic environment decreases or becomes extinct.Approximately 20 percent of the lakes in Scandinavia are without fish.Moreover, in Nova Scotia the【C2】______salmon industry may be threatened by the decrease of salmon in rivers and streams.The impact is also considerable in the waters of Ontario and Quebec, where fish populations are【C3】______the decline.
    What potential remedies exist for the acid rain issue? The experts disagree.Some say new environmental laws should be【C4】______to control the emission of pollutants in the atmosphere.Some say that if we had known how serious acid rain was, we would have planned better to prevent it.【C5】______, all agree that if the consumption of fossil fuel were reduced, we would have less of a problem.Another【C6】______is that special scrubbers could be installed in smokestacks to remove a good【C7】______of the pollutants before they get into the atmosphere.Other ideas even include breeding more tolerant fish.And research suggests that spreading lime into lakes may be effective in【C8】______acidity.In conclusion, it is clear that if we truly want to reduce the impact of acid rain, a【C9】______of remedies and international cooperation must be explored.It is a sad fact that acid rain probably could have been avoided if we【C10】______what we know now.
【C10】
选项 A、know
B、knew
C、had known
D、have known
答案C
解析 此处考查的是对过去事实的虚拟。因为主句是could have been avoided，从句应该用过去完成时(had done)，因此C项是正确答案。
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