名词性从句怎么选引导词

主语从句(The Subject Clause)

主语从句在句中作主语

1.主语从句位于句首时,会使句子显得笨邓咀挚垡重,因此常以it作为形式主语,而将主语从句后置,以保持句子平衡。如:

It is strange that she didn’t come yesterday.

2. whether与if引导主语从句的区别:

whether引导的主语从句既可放在句首也可放在句尾,if引导的主语从句只能放在句末。如:

Whether she comes or not makes no difference.

It is doubtful whether / if the President knew the details of the plan.

表语从句(The predicative clause)

表语从句在句中作表语,位于主句中的系动词之后。

1. 表语从句可用whether引导,也可用as if引导,但不能用if引导。如:

His first question was whether Tom had arrived yet.

It looked as if it was going to rain.

2. 主句的主语是reason时,表语从句要用that,不能用because。如:

The reason why he was dismissed was that he was careless and irresponsible.

宾语从句(The Object Clause)

宾语从句在句中作及物动词或介词的宾语。

1.在口语及非正式文体中,that常省略。

如:I thought he studied hard.

2.不能省略that的宾语从句

1)句中的动词后接两个或两个以上的that从句作宾语时,第一个that可省,但后面的that不可省。如:

He said (that) he couldn’t tell you right away and that you wouldn’t understand.

2) 当主句的谓语动词与that宾语从句之间有插入语时,that一般不可省。如:

Just then I noticed, for the first time, that our master was wearing his fine green coat and his black silk cap.

3) 当that从句是双宾语中的直接宾语时,that不可省。如:

I must never tell anyone that I could not see the cloth.

4) 当that宾语从句前有it作形式宾语时,that不可省。如:

We think it important that we study hard.

4. whether和if引导的宾语从句可以互换使用,但介词后的宾语从句只能用whether,不能用if。如:

He asked me if / whether my brother was at home.

It is a question of whether we should go.

同位语从句(The Appositive Clause)

同位语从句在句中作同位语,它一般要放在主句中某些名词的后面,说明这些名词的含义。

1.可跟同位语从句的名词主要有fact, news, promise, reason, idea等。

如:We heard the news that our team had won.

I have no idea how soon they are coming.

2. 同位语从句与定语从句的主要区别:

从意义上来说,同位语从句是对一个名词加以补充说明,定语从句对一个名词进行修饰或限定。从结构上说,同位语从句由连词引导,连词在从句中不作任何成分,只起引导作用;引导定语从句的关系代词在从句中担任一定成分,含有代替所修饰或限制词语的意义。

如:They were all shocked at the news that Germany had declared war on Russia. 他们都为德国向俄国宣战而感到震惊。(同位语从句,that只起引导作用,在句中不作任何成分。)

They were all shocked at the news that was announced on the radio. 他们都为收音机里宣布的消息而震惊。(定语从句,that在句中作主语,若省略that,句子成分不全。)