主语从句顾名思义(主句中的)主语是由一个句子充当。引导主语从句的连词有：who, whom, what, which, when, where, how, why, that , whether。
例如：1，Who will come doesn't matter.其中who will come 是主语从句。
2，What he said is funny.其中what he said是主语从句。
3，Which book was stolen is unknow now.其中which book was stolen是主语从句。
