is known to all is that effective measures should be taken to deal with the problem of th

is known to all is that effective measures should be taken to deal with the problem of the over-exploiting of our resources.
A. What
B. It
C. As
D. Which

(答案→)A. What B. ItC. AsD. Which解析：句意：众所周知的是应该采取有效的措施来处理过度开采资源的问题。分析句子成分可知，第二个is是谓语，前面的句子是主语从句，因为主语从句缺少主语，所以用what连接主语从句，It做的是形式主语，那么后面的is就要去掉，as引导的是非限制性定语从句，is就要改成逗号，which也是引导非限制性定语从句。选A。

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