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

问题补充：

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

Athat

B. when

C. what

D. why

答案：

(答案→)A. that

B. when

C. what

D. why

解析：考查宾表语从句的连接词。 you have to keep on being a success是表语从句，且从句句意完整，不缺成分，所以用that引导。 A。