__________ your valuable help, we couhtn't have finished the experiment ahead of time.

2023-08-04

A.If it were not for
B. Had it not been for
C.Were it not for
D.If it has not been for

参考答案:B

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,故选B。