Acid ran leads to fish mortality. Many species of fish cannot survive in aquatic environments there the PH is below 5.0. If the

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问题     Acid ran leads to fish mortality. Many species of fish cannot survive in aquatic environments there the PH is below 5.0. If the water is too acid, the gill systems of many kinds of fish can be damaged. 46 , the acid alters the blood chemistry of all fish. As a result, the fish population in an acidic environment decreases 47 becomes extinct. Approximately 20 percent of the lakes in Scandinavia are without fish. Moreover, in Nova Scotia the 48 salmon industry may be threatened by the decrease of salmon in rivers and streams. The impact is also 49 in the waters of Ontario and Quebec, where fish populations are on the decline.
    What potential remedies exist for the acid rain 50 ? The experts disagree. Some say new environmental laws should be enacted to control the emission of pollutants in the atmosphere. Some say that if we had known how serious acid rain was, we would have planne d 51 to prevent it. Nevertheless, all agree that if the consumption of fossil fuel were reduced, we would have less of a problem. Another 52 is that special scrubbers could be installed in smokestacks to remove a good 53 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 54 acidity. In conclusion, it is clear that if we truly want to reduce the impact of acid rain, a 55 of remedies and international cooperation must be explored. It is a sad fact that acid rain probably could have been avoided if we had known what we know now.

选项 A、Likewise
B、Besides
C、Thus
D、Otherwise

答案B

解析 备选项中A项:同样地,照样地,又,也,表示上下句的同类关系;B项:此外,表示下句对上句的补充;C项:因而,从而,如此,表上下句的因果关系;D项:另外,否则,不同地,别的方式,表上下旬的反义关系。依据该句大意,属于下句对上句补充,所以正确答案是B。
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