1．主语从句句首　　　 2．表语从句　　　　 3．介词之后

1．只要表示“命令、建议、要求”的各类名词性从句，都要用虚拟语气 should + 动词原形，should 可以省略。

2．在主语从句、表语从句或同位语从句中，也要注意主从句的谓语动词要一致，关键要注意动作发生的先后。

Who will win the first prize in the contest is not known to us.

Have you any idea why he was so rude?

1．在宾语从句中，当主句是一般现在时，其从句的谓语根据各种需要用各种时态

　　　　　 Mary is very diligent.　　　　　　　　　　 Mary was very diligent.

　　　　　 Mary is reading English.　　　　 Tom said　 Mary was reading English.

Tom says 　Mary will give us a talk.　　　　　　　　　 Mary would give us a talk.

　　　　　 Mary has been caught in the rain.　　　　 　　Mary had been caught in the rain.

　但是，宾语从句表示事实、格言、谚语等，从句的时态仍用一般现在时。

When he will arrive is not known.

I don't know how I can get through the exam.

3．连接副词有when, where, why, how 等，它们既起连接作用，本身又作从句的状语。

how many(much, far, long, often, soon)等引导主语、宾语、表语从句

2.连接代词有who, whom, whose, what, which, whatever, whoever, whichever等。它们在从句中起连接作用，本身又作从句的主语、宾语、宾补或定语。

1.从属连词有that, whether, if。它们只起连接作用，不充当从句的任何成分