虚拟语气if的三种用法是那些？

1、首先，是对将来情况的虚拟。例子：If he should go home,he would choose this road.

2、然后，是对现在情况的虚拟。例子：If he lived in HeiBei,he would know the enviornment.

3、最后，是对过去情况的虚拟。例子：If he had watched this TV show,he might have told me about this.