（3）引导从句作介词宾语时；

（4）从句后有"or not"时；

（5）后接动词不定式时。

E.g. Whether there is life on the moon is an interesting question. 月球上有没有生命是个有趣的问题。

　E.g. Everything depends on whether we have enough money. 一切要看我们是否有足够的钱。

　E.g. I wonder whether he will come or not. 我想知道他来还是不来。

　E.g. Can you tell me whether to go or to stay? 你能否告诉我是去还是留？

4.注意宾语从句中的时态呼应，当主句动词是现在时，从句根据自身的句子情况，而使用

　不同时态。

　E.g. He studies English every day.（从句用一般现在时）

　E.g. He studied English last term.（从句用一般过去时）

　E.g. I know (that) he will study English next year.（从句用一般将来时）

　E.g. He has studied English since 1998.（从句用现在完成时）

当主句动词是过去时态（could, would除外），从句则要用相应的过去时态，如一般过去时，过去进行时，过去将来时等；当从句表示的是客观真理，科学原理，自然现象，则从句仍用现在时态。

　E.g. The teacher told us that Tom had left us for America．

5.think, believe, imagine, suppose等等动词引起的否定性宾语从句中，要把上述主句中的动词变为否定式。即将从句中的否定形式移到主句中。

　E.g. We don't think you are here. 我们认为你不在这。

　E.g. I don't believe he will do so. 我相信他不会这样做。

二、表语从句

　表语从句：从句放在系动词be, look ,remain ,seem等之后即构成表语从句

引导表语从句的词有连词that，whether；连接代词who，what，which；连接副词when，where，how，why以及其它连词as if，as though，because等。

　E.g. The question is whether it is worth reading.

　E.g. They are just what I want.

　E.g. That's why they were late.

1.that引导的表语从句

that引导表语从句时，在句中无意义，一般不可省略。而what引导表语从句时，不但有意义，而且在从句中作主语、宾语、表语、定语等成分。

　E.g. The trouble is that I have lost his address.

　E.g. China is no longer what it used to be.中国不再是过去的样子了。

2.whether 引导的表语从句

whether 引导表语从句仍表示"是否"之意，不能在从句中充当句子成分。if则不可用来引导表语从句

　E.g. The question is whether they will be able to help us.

The question is whether the film is worth seeing.