既然你知道用钢笔写，为何还用铅笔呢？

活学巧用

2.单项填空

（1）He was walking along the sands________ he saw a big footprint in the sand.

A.while B.when C.as D.which

提示：sb.be doing sth.when..."某人正干什么这时......"。

答案：B

（2）(2005上海高考，34) He transplanted the little tree to the garden________it was the best time for it.

A.where B.when C.that D.until

提示：when引导时间状语从句，句意是："他在最适宜的时节，把小树移植到花园里。"

答案：B

（3）(2005福建高考，24)

-Did Jack come back early last night?

-Yes.It was not yet eight o'clock ________ he arrived home.

A.before B.when C.that D.until

提示：when引导时间状语从句。句意是："他到家时还不到八点。"

区别：It was at eight o'clock that he arrived home.（强调句）

答案：B

（4）You can turn to him for help ________you need help.

A.when B.while C.before D.until

提示：句意"如果你需要帮助可以向他求助。"when作"如果"讲。

答案：A

3.What it really means to be a gentleman is an important theme in Great Expectations.

成为一个真正的绅士意味着什么，这是《远大前程》的一个重要主题。

【剖析】what it really means to be a gentleman是主语从句，what作means的宾语。

【归纳】（1）主语从句在复合句中作句子的主语。引导主语从句的词有：连词that,whether；连接代词who,that,which；连接副词when,where,how,why等。其中that不作句子成分。如：

What he wants is a book.他想要的是一本书。

When we shall have our sports meet is still a question.

我们什么时候开运动会还是个问题。

（2）主语从句可以直接放在句首，也可用it作形式主语，而将从句放在句末。常见的用it作形式主语的复合句结构：

①It is+名词+that从句

It is a fact(a shame,a pity,no wonder,good news,...)that...

②It is+形容词+that从句

It is necessary(strange,important,wonderful,possible,likely,...)that...

这类主语从句中，谓语动词多数为"（should）+动词原形"。

③It is+过去分词+that从句

It is said(reported,decided,...)that...

④It+不及物动词+that从句