主语的形式一句话中主语除了为人称代词、人名、国名还可以为什么样的单词

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名词、代词、数词、主语从句、doing ,to do都可以作主语
如：The boy is clever.
He is a student.
One is enough.
What he said is right.
Doing morning exercises is good for us.
To read in the morning is necessary.