1.if 可引導狀語從句
如果...,假使...
a.[就現(xiàn)在,過去,未來可能實現(xiàn)之事加以推測時]
If you are tired,we will go straight home 如果你疲倦了,我們就直接回家
If you have finished reading this book,please return it to me 如果你念完這本書,請把它還給我
Do you mind if I open the window?如果我打開窗子,你介意嗎?
(我可以打開窗子嗎?)
I shall tell him if he comes 如果他來了,我會告訴他
2.用于虛擬語氣中
a.If you knew how I suffered,you would pity me 如果你知道我多麼受苦,你會同情我
If I were you,I would help him 如果我是你,我會幫助他
b.If I had known,I wouldn't have done it 假使我知道,我就不會做那件事
If he had followed my advice,he wouldn't be in such difficulty now 如果他聽從我的勸告,他現(xiàn)在就不會陷入如此的困境
c.If it should rain tomorrow,I shall not [shan't,won't] come 萬一明天下雨,我就不來
3.if可引導賓語從句 ,"是不是..."基本等同于whether
Ask him if it is true 問他那是不是真的
I wonder if he is in the school 我不知道他是否在學校