问题补充：
a certain doubt among the workers as to whether he could finish the task in a short time．
A. It was
B. There had
C. There existed
D. It had
答案：
A. It was
B. There had
(答案→)C. There existed
D. It had
解析：There existed为there be句型的变体意为“有”。句意：关于他是否能在短时间内完成这项任务在工人中存在着某种怀疑。
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