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

问题补充：

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：

(答案→)A. What

B. It

C. As

D. Which

解析：考查名词性从句。分析题干结构“ is known to us all”是主语从句，从句中缺少主语，what 引导主语从句，在从句中作主语。如果选 it，需去掉 all 后的 is，如果选 as需去掉 is that。句意为“众所周知，面对过度开发资源的问题，我们应该采取有效的措施。” as 作为关系代词引导的非限制性定语从句位于主句之前时， It从句与主句之间要用逗号隔开。作为形式主语将 that 引导的主语从句后置时，that 常常不能省。选A。