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efore既是介词又可以作为引导时间状语的重句的连词,更可以做副词.
1作为介词,那么后面出现动词需要用动词ing形式,因为介词后面一般都是名词.比如:You mustn't hang out before finishing your assignment.
2before作为连词.Make sure that you lock the door before you leave the room.但有点需要注意,就是如果从句是过去式,那主句需要用过去完成式.I had been there for more than 15 years before I decided to depart for China.
3before作为副词.I have never met that man before.
1年前
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