1、before后面直接跟动词的，那个动词就用ing形式
例如：I go to the WC at first before going home.在回家之前先去趟厕所
before后面有宾语的，其后动词就用原形
例如，I clean the room at first before you come here.在你来这儿之前我先打扫一下房间.
2、用于It+be/take+时间段+before句型
在这一句型中又可以根据主从句的时态分成两种情况。
若主句是一般时将来时态，从句是一般现在时.若主句是肯定句意思是“要过多长时间才”若主句是否定形式翻译成“用不了多久就”。
It will be two weeks before everything returns to normal.
两周之后一切才能恢复正常。
It will be many years before the situation improves.这种状况或许要过许多年才能得以改善。
这时若主句是一般过去时从句也是一般过去时。若主句是肯定句翻译成“多长时间之后才”，若主句是否定形式翻译成“没过多久就”。
如：
It was some time before I realized the truth.过了很长一段时间我才了解到真相。
It wasn't long before she became a brave solider.没过多久她就成了一名勇敢的战士。
After that it still took seven years before they got married.他们又过了七年才结婚。
before加动词和句子的用法
before加句子 ，表示在……之前。before加动词的时候要加ing形式。例如：
1、 We will hold a meeting before we have a discussion about the problem.
2、Before he came to my home，he bought a cake.
3、Before having lunch，he finished writing a letter to his girlfriend.
4、Before making a conclusion，we should listen to her explanation.
