先举例再说明:when he was asked where to go ,he kept silent.这个句子里when引导的时间状语从句 和主句都是he,那么可以省掉when后面的he,但是同时要改变从句的谓语,变成非谓语,是be动词的话, 直接省略,上句可改为when asked where to go ,he kept silent 如果从句谓语不是be动词,就要根据从句谓语与主语的关系相应变成现在分词和过去分词,如: once you find the truth,you will feel surprised=once finding the truth,you will feel surprised