_______,our experiment would have failed．A．Should he not help us B．Did he not help us C．Had he not helped us D．If he has not helped us
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_______,our experiment would have failed．A．Should he not help us B．Did he not help us C．Had he not helped us D．If he has not helped us
_______,our experiment would have failed．
A．Should he not help us
B．Did he not help us
C．Had he not helped us
D．If he has not helped us
_______,our experiment would have failed．A．Should he not help us B．Did he not help us C．Had he not helped us D．If he has not helped us
C
D
c
c,虚拟语气
C
由后一句我们的实验将会失败（而且此句用了过去将来完成时），可知前面应该用过去完成时了，因为省略了if所以had提前，句子倒装。
c
C,后面是过去将来完成时，虚拟语气，对应的是过去完成时。
过去将来完成时态的基本的用法
1）表示在过去将来某时间以前发生的动作，并且会对过去将来某一时间产生影响。
He told me he would have finished it by 9.
他告诉我他将在9点钟的时候完成。
2）用在虚拟语气
If you had not helped me,...
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C,后面是过去将来完成时，虚拟语气，对应的是过去完成时。
过去将来完成时态的基本的用法
1）表示在过去将来某时间以前发生的动作，并且会对过去将来某一时间产生影响。
He told me he would have finished it by 9.
他告诉我他将在9点钟的时候完成。
2）用在虚拟语气
If you had not helped me,I would not have succeeded.
如果你不 帮我，我 是不会成功的。
http://www.grammarspot.com/html/Tenses/Perfect_tense/20070827/258.html
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C