______ your valuable help, we couldn't have finished the experiment ahead of time.
A、
If it were not for
B、
Had it not been for
C、
Were it not for
D、
If it has not been for
【正确答案】
B
【答案解析】
考查虚拟语气。本题是与过去事实相反的虚拟语气，如果省略if，句子要倒装，倒装时要将助动词提前，因此正确答案为B。
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