_____,I would not have rushed to his help.A.If_____,I would not have rushed to his help.A.If I knew B.If I know C.Have I known D.Had I known正确答案是D,求解为什么选D

问题描述:

_____,I would not have rushed to his help.A.If
_____,I would not have rushed to his help.
A.If I knew B.If I know C.Have I known D.Had I known
正确答案是D,求解为什么选D