isknowntoallisthateffectivemeasuresshouldbetakentodealwiththeproblemoftheover­exploitationofourresources.A．WhatB．ItC．AsD．Which

Question

________ is known to all is that effective measures should be taken to deal with the problem of the over­exploitation of our resources.

A．What	B．It
C．As	D．Which

Answer 1

A

选A　考查主语从句。分析句子结构可知，空处引导主语从句，且在从句中作主语，所以用what引导。注意区分以下结构：As is known to all, effective measures should be ...，其中As引导非限制性定语从句；It is known to all that effective measures should be ...，其中It为形式主语，真正的主语是that引导的主语从句。