The toughest thing about success is you have to keep on being a success.A. whyB. whenC. w

问题补充：

The toughest thing about success is you have to keep on being a success.

A. why

B. when

C. what

D. that

答案：

A. why

B. when

C. what

(答案→)D. that

解析：考查名词性从句。此题是一个表语从句，that 不做任何成分，只起连词的作用。句意：关于成功最难的事就是你不得不继续当一个成功的人。所以选D。