在名词性从句中,什么时候该用what；什么时候该用that【最好有举例】

what在从句中充当主语,宾语或表语,意思是“什么”或“所.的”.that在从句中不充当成分,无意义.如：What you said didn't agree with what you did.2.She doesn't know what he should do.3.That he passed the exam made him very happy.4.His suggestion is that the meeting should be put off .