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
_____,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
问题解答：
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