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　think about, think of, think over这几个短语都和think有关，主要去别在于意思不同，所以用法也就不同。 think 意思是“ 想，以为，思索”think 既可以作及物动词也可作不及物动词。 如：1）Think before you act ．先思而后行。2）The teacher told me to try to think in English ．老师让我们试着用英语思考。 think about指“考虑，回想，想起” 如： 1）He is thinking about travelling in the summer holidays. 他正在考虑暑假旅游的事。 2）She was thinking about her childhood days. 她正回想她的童年时期。 think of指“考虑，计及，记忆，记起” 如： 1）You think of everything! 你全都提到了。 2）I can't think of his name at the monment. 我一时想不起他的名字。 think sth. over指“仔细想，审慎思考，作进一步考虑” 如： 1）Please think over what I said. 请仔细考虑我说的话。 2） I want to think it over. 我想仔细考虑一下这件事。

If译为如果,可以做从句,中的引导词,For作为,介词