单选题
______ is known to all is that effective measures should be taken to deal with the problem of the over-exploitation of our resources.
【正确答案】
A
【答案解析】 句意：众所周知，过度开发资源带来的问题需要用有效的方法来解决。空格引导从句在整个句子中充当主语，句中真正的主语是“effective measures should be taken to deal with the problem of the over-exploitation of our resources.”，由于从句中缺乏主语，所以用关系代词what来代替真正的主语，故选A。