The sentence you provided is not complete and lacks context, but it seems like you're trying to express uncertainty about someone coming. A more grammatically complete and clear version might be:
"Whether he will come is doubtful."
If you meant to start the sentence with a conjunction or introductory phrase, it could look like this:
"If he comes is doubtful," or "That he will come is doubtful."
Please provide more context if you need a more specific correction or completion of the sentence.
( ) he will come is doubtful.
A. If
B. Whether
C. That
D. What
B
解析
分析句子结构可知,本句为主语从句,空格处应填入意为“是否”的词,排除C、D两项。if引导的主语从句不能位于句首,所以排除A项。故选B。