We can see no clouds in the sky. Therefore there’s no doubt it will be fine tomorrow.A.

问题补充：

We can see no clouds in the sky. Therefore, there’s no doubt it will be fine tomorrow.

A. that

B. whether

C. if

D. how

答案：

(答案→)A. that

B. whether

C. if

D. how

解析：考查固定句式。固定句式；There is no doubt that…毫无疑问…that引导的是一个同位语从句，来解释名词doubt的内容；句意：毫无疑问明天的天气会很好。故A正确。