if后面跟什么时态

问题描述:

if后面跟什么时态

if作如果讲时后面主句用的是将来式或者情态动词如:We'll go to the mountains if the weather is fine tomorrow.if作是否讲时,后面跟的事态随主句变化,与whether可以互换如:I don't know if he will come tomorrow...