虚拟语气TODO

if条件状语从句

过去事实的虚拟

从句过去完成时(had+done)，主句(should,would,could,might) + (have+done) 现在完成。

对过去的事实进行虚拟 + 从句助动词倒装

1. The accident wouldn’t have happened had the weather been better.
2. Had he put on his seatbelt, he might not have been injured so badly.