请看下面例句的不同含义：?

限制性：她有两个当解放军的儿子。?

She has two sons who are P.L.A.men.?

(Maybe she has other sons who are not P.L.A.men.)?

非限制性：她有两个儿子，他们都是解放军。?

She has two sons，who are P.L.A.men.?

(She has only two sons.They are both P.L.A.men.)?

体会下列非限制性定语从句?

Yesterday I met Li Ping，who seemed to be busy.?

昨天我遇到了李平，他看起来?很忙。??

We will put off the meeting until next week，when we won’t be so busy.?

我们将把会议推迟到下周举行，到那时我们就不会这么忙了。

2.关系代词which与as引导定语从句的区别?

which与as都可以引导定语从句，但它们有许多用法上的区别，现就此简要分析如下：??

1)which与as引导非限定性定语从句的区别：?

which只能放在主句后面，而as引导的从句位置相对较灵活，可在前，可在后。如：?

As he realized，I was very useful to him.?

(在前)正像他所意识到的那样，我对他非常有用。?

Air，as we know，is a gas.(在中)空气，众所周知，是一种气体。?

He was a foreigner，as I know from his accent.?

(在后)他是个外国人，正像我从他的口音判断的那样。?

He came late again，which made his boss angry.?

(在后)他又来晚了，这一点使得老板很生气。?

在which引导的定语从句中，谓语动词若是am，is，are，则这些系动词不能省略，而as后面若是这种情况，则可以省略。如：?

He is a teacher，as (is)clear from his manner.(is可以省略)他是个老师，这从他的言谈举止可看清楚。?

He said he had never seen her before，which was not true.?

(was 不可省略)他说他从来没见过她，这一点不对。?

当which引导的从句在意义上近乎并列关系时，可以用and this，and that代替，意思是“这件事”。如：?

He changed his mind，which (and this，and that)made me very angry.?

他改变了主意，这使我很生气。?

She has married again，which (and this，and that)was unexpected.?

出乎意料的是，她又结婚了。?

而as主要起与上下文连接的作用，表达说话人的看法、观点，并指出主句内容的出处或根据等。如：?

Einstein，as we know，is a famous scientist.爱因斯坦，众所周知，是位伟大的科学家。?

As is announced in today’s newspaper，we must improve our style of work.?

今天的报纸上说，我们必须改进工作作风。?

作主语时，which既可以作系动词be的主语，也可以作实义动词的主语，而as只可以作系动词be的主语。如:?

He married her，which was natural.?

(可用as代替which)他和她结婚，这是很自然的事。??

He won a/the Nobel Prize in chemistry，which made him illustrious.?

(不可用as代替which)他获得了诺贝尔化学奖，这使他名扬天下。?

当定语从句位于主句之后，纯粹表示主句所述的内容，不带有“如……那样”的意思时，往往用which，而不用as。如：?

They were invited to the state banquet，which was a great honor to them.?

他们被邀请参加国宴，这对他们来说是莫大的荣幸。?

We had to sleep in our wet clothes，which was most uncomfortable.?

我们不得不穿着湿衣服睡觉，这简直太不舒服了。?

Mummy always treats me just like a baby，which I can’t bear.?

妈妈老把我当成小孩子对待，这让我无法忍受。?

当定语从句有“如同……那样”的意思时，用as比用which更常见，而这些从句几乎成为固定说法。如：

Things will turn out contrary to one’s wishes，as is often the case.?

事与愿违，这是常有的事。?

As was natural， this inordinate hope was followed by an excessive depression.?

这种过分希望之后，接着是极度的沮丧，是很自然的事。?