if是否的用法

例句：

I could do it now, if you like.

如果你願意的話，我現在就可以做這事。

You can come with us if you want to.

如果你願意可以跟我們一起來。

Put your hand up if you need more paper.

若有人還要紙，請舉手。

Only time will tell if the treatment has been successful.

只有時間才能證明這種療法是否成功。

He must be 70 if he's a day!

他至少70歲了！