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（ ）for their help, we couldn't have finished the task ahead of time.
A、If it were not
B、Hadn't it been
C、Had it not been
D、If it was not
【正确答案】：C
【题目解析】：if 省略，从句部分倒装，句子含义是要不是他们的帮助，我们不可能提前完成任务。