1.动名词和不定式作主语
v-ing通常表示已知的事实或曾经做事
to do通常表示一种意愿、目的或未完成的事
注意：不定式或动名词做主语时往往会形成主语太长的现象故通常用代词it
例如：Collecting stamps is one of his hobbies.
It's one of his hobbies to collect stamps
It 是形式主语 collect stamps 是真正主语
2.名词性从句作主句
（1）That从句
That he doesn't study makes me angry.
It makes me angry that he doesn't study.
（2）Whether从句
从句可用ye/no回答的问句变化而成，这种可用yes/no回答的问句称为一般疑问句。
a.问句有be动词或一般助动词（can,will,may,should,ought to）
例如：Has he done It?
Whether he has done it?
b.问句有do,does,did等助动词时
例如：Did he come?
Whether he come?
（3）疑问词引导的从句（when,what,how,where,why）
a.问句有be动词时
what is he doing?
what he is doing
b.问句有一般助动词时
where can he find it?
where he can find it.
c.问句有do,does,did等助动词时
what did he write?
what he wrote.
注意：who,what,which为疑问代词时
①who came here
②what happened
③which was bought
变为名词性从句时，结构不变
3.名词性短语作主语
（1）疑问副词
a.where to live
b.when to talk to him
c.where to try again
d.how to do It
（2）疑问代词
a.what to do
b.which to buy
c.whom to see
d.whom to talk to
4.表示距离的地点副词短语作主语 （from..... to......）
例如：From Shanghai to Beijing is about 1000 kilometers.
It's about 1000 kilometers from Shanghai to Beijing.
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