可以
1.可引导状语从句
如果...,假使...
a.[就现在,过去,未来可能实现之事加以推测时]
If you are tired,we will go straight home 如果你疲倦了,我们就直接回家
If you have finished reading this book,please return it to me 如果你念完这本书,请把它还给我
Do you mind if I open the window?如果我打开窗子,你介意吗?(我可以打开窗子吗?)
I shall tell him if he comes 如果他来了,我会告诉他
2.用于虚拟语气中
a.If you knew how I suffered,you would pity me
如果你知道我多麽受苦,你会同情我
If I were you,I would help him 如果我是你,我会帮助他
b.If I had known,I wouldn't have done it 假使我知道,我就不会做那件事
If he had followed my advice,he wouldn't be in such difficulty now 如果他听从我的劝告,他现在就不会陷入如此的困境
c.If it should rain tomorrow,I shall not [shan't,won't] come 万一明天下雨,我就不来
3.if可引导宾语从句
,"是不是..."基本等同于whether
Ask him if it is true 问他那是不是真的
I wonder if he is in the school 我不知道他是否在学校
