1. 由陈述句充当宾语从句时，用that引导，that无实在意义，在口语和非正式文体中常省略。

 Miss Liu said ______ she would leave the message on the headmaster”s desk.

A. that B. where C. which D. what

2. 由一般疑问句充当宾语从句时，用if或whether引导，意为“是否”。

 I don”t know ______ he still lives here .

A. where B. what C. when D. whether

 In the bookshop , a reader asked the shopkeeper ______ Who Moved My Cheese was an interesting book.

A. that B. how C. what D. if

当if和whether（表示“是否”）引导宾语从句时，应注意以下几种情况：

a.介词之后的宾语从句，只能用whether连接，而不用if.I’m interested in whether he’ll go

b. 宾语从句中的whether与or not直接连用时，就不能换成if；

I don’t know whether or not you will go.

c. 动词不定式之前，只能用whether。He doesn’t know whether to visit that old man again.

d. 宾语从句置前时，只能用whether.  Whether he lives there, I want to know.

Tell me ______ you will go with us or stay at home.

A. if          B. whether         C. that       D. how

剖析:引导宾语从句时,if和whether常可以互换,但有些情况是不能互换的?当从句中提出了两种选择,或从句位于介词后面,只能用whether