7.it的用法

①用作人称代词,代替前文提到的事情。

This bike is not mine. It’s Peter’s.

②用以代替提示代词this, that

-What is this?　　　　　　 -It’s a pen.

-Whose book is that?　　　 -It’s Mike’s.

③起指示代词的作用,指一个人或事物

-Who is knocking at the door?　　　 -It’s me.

-Who is making such a noise.　　　 -It must be the children.

④指环境情况等。

It was very quiet at the moment.

⑤指时间，季节，天气，气候等

-What time is it?　　　　 -It is eight o’clock.

It often rains in summer.

⑥指距离

It is five kilometers from the office to my home.

It is a long way to the factory.

⑦作形式主语和形式宾语

当动词不定式,动名词或从句作主语时,通常把它们放在谓语之后,而用it作句子的形式主语

It is not easy to finish the work in two days.

It is not a good habit to stay up late.

It is no use crying over split milk.

It is a pity that you didn’t read the book..

当复合宾语中的宾语是不定式,动名词,宾语从句时,往往把宾语放在它的补足语后面,而用it作形式宾语,放在宾语补足语之前

I think it no use arguing with him.

I found it very interesting to study English.

He made it clear that he was not interested in this subject.

注意：see to it that…(务必)和take it for granted that…(想当然)句型中的it，以及词组make it

中的it(做事成功，搞定)。

⑧用于强调结构(详见专题九)

要强调句子的某一部分(通常是主语,状语,宾语), 可以把it 当作先行词.这种句子的结构是 “It is(was)+被强调部分+that (who )+句子的其余部分” .如果强调的部分是人,可用who whom 代替that

I met an old friend in the park yesterday.

此句各部分被强调后句型如下：

It was I who /that met an old friend in the park yesterday.

It was an old friend who/ that/whom I met in the park yesterday.

It was in the park that I met an old friend yesterday.

It was yesterday that I met an old friend in the park.

(二)数词

数词分两类：基数词和序数词

6.不定代词

不定代词种类较多,在使用时应注意其用法与区别。为了便于记忆我们择其重点以表格的形式列出。

5.相互代词

①在句中可作宾语

They help each other and learn from each other.

②加’s后成为所有格,作定语

They asked about one another’s life and work.

4.指示代词

①this和that是近指, that和those 是远指

I don’t want this book. I want that one.

②有时为了避免重复,常用that/ those 来代表前面出现过的名词

At this time of year, the weather here is much colder than that in Nanjing.

③this和that都可代表前面提到过的事情,若出现两个名词,指代前面的用that指代较后面的用this；但若指下文将要叙述事情,则只能用this，不能用that。此外，还可用于代替上文中出现过个单数或不可数名词，且后面带有of短语修饰。

Health is above wealth; this cannot give so much happiness as that.

健康胜于财富;财富不会像健康那样带来那么多幸福(句中this=wealth;that=health)　

They cant afford it.That/this is their problem.

What I want you to remember is this :English is of great use.(此句中this不能用that替换)

The population of Shanghai is larger than that of Suzhou.

④such的用法

such 一般在句中作定语和主语.用作定语时,它所修饰的名词前的不定冠词应放在之后。

Such is my answer.

Such are the results of the exams.

I have never seen such beautiful flowers.

用作定语时,它所修饰的名词前的不定冠词应放在such之后such a good book。

3.反身代词

①用作宾语、表语，或主语、宾语的同位语

He teaches himself Japanese every evening.(宾语)

She is not quite herself today.她今天身体不太舒服。(表语)

I myself can repair the bike.(主语的同位语)

②常用含有反身代词的惯用语归纳

by oneself= alone 独自　　　　　　　　　　　　　 for oneself独立、为自己

be oneself处于正常状态,显得自然　　　　　　　　 enjoy oneself玩得愉快

seat oneself坐下　　　　　　　　　　　　　　　　 dress oneself in 给自己穿

devote oneself to专心于、献身于　　　　　　　　　 help oneself to 自行取用、不用客气

come to oneself苏醒　　　　　　　　　　　　　　 make oneself at home 不要客气

2.物主代词

①形容词性物主代词只能作宾语

We love our motherland.

②名词性物主代词可用作主语,表语和宾语

Your coat is black while mine is red.

1.人称代词

①在句中作主语,用主格，在句中作宾语,则用宾格；

She teaches them physics.

②在句中作表语,常用宾格；

Who is it? It’s me.

但有时要用主格：It was I who told him the whole story.

在强调句型中,强调的是主语,故I用主格。

③两个或两个以上的人称代词并列时,其顺序是：

单数按2,3,1人称排列，复数按1,2,3人称顺序排列。

you, she and I ; we, you and they

20.(本小题共14分)

已知椭圆 的焦点是 , ,点 在椭圆上且满足 .

(Ⅰ)求椭圆 的标准方程；

(Ⅱ)设直线 与椭圆 的交点为 ， .

(i)求使 　的面积为 的点 的个数；

(ii)设 为椭圆上任一点， 为坐标原点， ，求 的值.

北京市宣武区2009~2010学年度第二学期第二次质量检测

19. (本小题共14分)

设 是正数组成的数列，其前 项和为 ，且对于所有的正整数 ,有 ．

　(I) 求 ， 的值；

　 (II) 求数列 的通项公式；

　(III)令 ， ， ( )，求 的前20项和 ．