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
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(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。