It is human activity has caused this global warming.A. whichB. thatC. whatD. why

问题补充：

It is human activity has caused this global warming.

A. which

B. that

C. what

D. why

答案：

A. which

(答案→)B. that

C. what

D. why

解析：考查强调句。根据句子结构可知该句为强调句，强调句的特点是去掉it is ……that 之后，句子结构完整，即human activity has caused this global warming.