It is not clear the effects of global warming will be.A. howB. whichC. thatD. what

问题补充：

It is not clear the effects of global warming will be.

A. how

B. which

C. that

D. what

答案：

A. how

B. which

C. that

(答案→)D. what

解析：考查名词性从句的主语从句。本题的it是形式主语，真正的主语是what the effects of global warming will be. what在句中做表语。句意：全球变暖的影响是什么现在还不清楚。故D正确。