可数单数用one替,ones替代复数词.
不定冠词后加one,one前一般有定语.
替代若系本身物,it 替单 they 代复.
比较句中替代词,不可数名词that替.
最高级及序数词后,替代词常常被略去.
复数名词替代词,ones 与 those 均用之,
特指 ones 加定冠,those 之前无冠词.
One(s) 的定语多在前,those 的定语必后置.
一、It用作实词
表达以下概念:指代前文提到的事物,前文中的this,that；替代前文中的内容；指代一位性别不明的小孩或未知的人；指代未指明但谈话双方都知道的那件事；指代时间、天气、气候、距离等自然现象.
二、It用作形式主语
替代作主语的从句、动词不定式、动名词,而把真正作主语的从句、动词不定式、动名词置于句尾.
It 作形式主语的常见句型：1.代作主语的动词不定式,其句型为（1）It be adj.(for sb.) to do sth.
（2）It be adj.of sb.to do sth.
（3）It替代作主语的动名词的常见句型：
It’s no good/use doing…
It’s (well)worth doing…
It’s (well)worth one’s while doing/to do It’s (well)worth while doing/ to do
2.It替代作主语的从句常见句型
（1）It is + noun +从句
（2）.It is adj.+clause
It’s surprising that… (should)………竟然……
It’s a pity/shame that…(should)………竟然…
（3）It verb sb.+ clause= It is v-ing + clause
It+surprise/delight/interest/disappoint/worry/disturb/annoy/amaze/bother/concern/frighten/please/anger sb.that…
（4）It verb (to sb.) that…= sb/sth verb to do
(verb = appear,seem,come about,emerge,follow,chance,happen,occur,transpire,turn out ,work out)
（5）It is v-ed that…=sb/sth is to do
(verb=say,report,think,believe,hope,expect,agree,accept,decide,determine,intend,plan,understand,know）
四、It 作形式宾语
用来替代作宾语的从句、动词不定式、动名词,而把真正作宾语的从句、动词不定式、动名词置于句尾.
It 作形式宾语的常见句型：
1.verb+ it+ adj./noun (for/of) to do/clause (verb=think,believe,suppose,consider,feel,make,keep…)
that 用法
pron.
1.那;那个,那人,那事,那东西
That's my English teacher over there.
那边是我的英文老师.
2.(已被提到的)那个,那人,那事,那东西
Who told her that?
那是谁告诉她那件事的?
3.前者
4.(用作关系代词的先行词)那,那个
What is that which you have just stuffed into the plastic cup?
你刚才塞在塑料杯里的是什么东西?
5.(代替句中名词,避免重复)
The output of steel this year has increased by 20% compared with that in 1992.
今年钢产量比一九九二年增长了百分之二十.
6.(用作关系代词,引导关系从句)
a.
1.那,那个
That book isn't mine.
那本书不是我的.
ad.
1.【口】那样,那么
Is the problem that easy?
问题有那么简单吗?
conj.
1.(引导名词从句)
He expressed the hope that we would keep in touch with his firm.
他表示希望我们与他的公司保持联系.
My idea is that we should act on his suggestion.
我的意见是我们应当按照他的建议去办.
That she is still alive is a relief.
她还活着,这是令人感到宽慰的.
2.(引导状语从句,表示原因或理由)因为,由于
We are glad that we have accomplished another arduous task.
我们都感到高兴因为又完成了一项艰巨的任务.
3.(引导状语从句,表示目的或结果)为了,以至于
He is working hard that he can catch up with the class.
他努力用功,以便赶上班上同学.
4.(引导表示愿望,感叹的从句,主句常省略)
That I could stay at home today!
今天要是我能呆在家里多好呀!
