___a few minutes earlier,the pollicemen would have caught the murderer.

问题描述:

___a few minutes earlier,the pollicemen would have caught the murderer.
A.If they arrived
B Had they arrived
为什么不选A?选B

这是if 引导的虚拟从句 是对过去的虚拟 从句省略if 用了倒装 完整的语句是if they hadarrived a few minutes earlier