如果一个句子在复合句中充当一个主语,那么这个句子就是主语从句.
常规主语从句,即句子在复合句中充当一个主语
"（7）Whose watch was lost is unknown."
（1）That he finished writing the composition in such a short time surprised us all.
（2）Whether we will go for an outing tomorrow remains unknown.
（3）Who will be our monitor has't been decided yet.
（4） Whom we must study for is a question of great importance.
（5）What caused the accident remains unknown.
（6）Whatever you did is right.
（7）Whose watch was lost is unknown.
（8）What we need is time.
（9）What we need are good doctors.