There is no doubt we will succeed if we try our best.A. whichB. whatC. whetherD. that

问题补充：

There is no doubt we will succeed if we try our best.

A. which

B. what

C. whether

D. that

答案：

A. which

B. what

C. whether

(答案→)D. that

解析：考查固定句式。固定句式:There is no doubt that…毫无疑问…that引导是一个同位语从句，介绍名词的内容。因为no doubt表示的是一个确定的陈述的事实，故使用that引导。Whether引导的是一个表示疑问的句子。记忆：毫无疑问国际合作是对付网络犯罪的关键。故B正确。