if是否的用法

例句：

I could do it now, if you like.

如果你愿意的话，我现在就可以做这事。

You can come with us if you want to.

如果你愿意可以跟我们一起来。

Put your hand up if you need more paper.

若有人还要纸，请举手。

Only time will tell if the treatment has been successful.

只有时间才能证明这种疗法是否成功。

He must be 70 if he's a day!

他至少70岁了！