before doing与before do

before doing与before do before doing和before to do before doing sth 和 before you do sth,为什么? before sb doing还是do sth before doing sth还是do sth before doing sth BEFORE DOING和AFTER help,open的过去分词是什么?是before sb do sth.还是before sb doing sth... before long与long before before 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 before doing除了before还有什么类似的?