1、that引导陈述句，只起连接作用，在句中无词义，不充当句子成分，多数情况下可以省略。例如I know (that) he is a teacher
3、疑问词what, who, whose, when, where, how, why, whoever,等引导特殊疑问句，例如the teacher doesn't know why he comes late
5、如果宾语从句表示的是客观真理，那么不管主句是什么时态，宾语从句都用一般现在时，例如the teacher told us yesterday, that the moon travels round the earth once every day
