用after或before

用before还是after? 用before或after连接过去的两个句子时,before 和after各用什么时态 请问after和before后面的动词要用ing吗?比如after he leaving 或before he leav 用since,as,when,as soon as,while,if,after,before,until或becaus after&before before after before和after一定要用过去式吗? 英语翻译要用.after..before..but. 用连词if,when,after,before填空. after和before while after before when since,before,after