宾语从句,动词介词之后.引导词：疑问词和that,that可省略.表语从句,系动词,be动词之后.引导词：疑问词和that,that不可省略 .主语从句,1 句首,疑问句或that+完整句子.2 It+动词+疑问词/that.引导词：疑问词和that,tha...