2.与过去事实相反的假设

若表示与过去事实相反的假设，从句中用过去完成式，主句中用“would/ should/could/might+have+过去分词”。

The soup would have been better if it had had less salt．

要是汤里的盐少点的话，味道会更好些的。

If I had had insurance，the sickness wouldn't have caused such a big problem．(人教大纲版高三第75页)

要是我办了保险，这个病就不会引起这么大的问题了。

She would/might have come if she hadn't been so busy．

她要是不那么忙的话，就可能来了。

If I hadn't taken your advice，I would have made a bad mistake．

我要是不听你的建议的话，就会犯严重错误的。

If I had known more about giving first aid，I could have helped them．(人教大纲版高二上第59页)

如果我多懂一点急救知识，就能帮助他们了。