求 before doing sth的用法?He was sad before doing sth.就是before doing sth 前可以不可以用过去时态.不行的话,那应该如何表示 去电影院前,我去了图书馆.是过去时态.

求 before doing sth的用法?He was sad before doing sth.就是before doing sth 前可以不可以用过去时态.不行的话,那应该如何表示 去电影院前,我去了图书馆.是过去时态. help,open的过去分词是什么?是before sb do sth.还是before sb doing sth... before doing sth还是do sth before doing sth 和 before you do sth,为什么? 求perfer的用法（有一点一定要讲,perfer doing sth to doing sth /perfer doing sth to do sth ） before什么时候加doing sth./sb.do sth.什么时候before后加一般过去时的句子或过去完成时的句子 before doing sth before making a decision,think it over.为什么用making? 求与succeed in doing sth意思一样的词组succeed in doing sth= = . keep sb./sth.doing sth.和keep sb./sth. +形容词的区别 求例句 求些英语句子组合比如is doing sth ；sb to do sth；enjoy doing sth这样的 用这些造英语句子 finish doing sth keep doing sth avoid doing sth delay doing sth excuse doing sth admit doing sth report doing sth appreciate doing sth deny doing sth explain doing sth 用英语造句 求 doing sth 的常见短语包括中文 求教because doing sth.的用法,求具体~ before sb doing还是do sth如题``` What about doing sth?的doing sth做主语吗? prefer doing sth to doing sth 的用法~ up doing sth 和 stop doing sth 的辨析