it ⼀that⼀one的区别

I. it／one ／that三者均可用作代词, 指代前面提到的名词。一般说来, it指代同名同物; one与that则指代同名异物。
I have lost my umbrella; I'm looking for it. （该句中it就是指前面的my umbrella）
I have lost my umbrella; I think I must buy one. （one在该句中表泛指, 因为my umbrella已经丢了）
The umbrella you bought is cheaper than that I bought. （替代词that在该句中特指“the umbrella I bought”, 以区别“the umbrella you bought”）
II. one与that虽可用来指代同名异物, 但one为泛指, 相当于a／an＋名词; that为特指, 相当于the ＋名词。所以one所指代的名词的修饰语一般为 a／an ／some ／any; that所指代的名词的修饰语往往是the ／this ／that。
A chair made of steel is stronger than one made of wood. （该句中one可以换成a chair）
The water in the cup is hotter than that in the pot. （该句中that可以换成 the water）
III. one只能代替可数名词单数, 代替可数名词复数时用ones; that既可以代替不可数名词也可以代替可数名词单数, 代替可数名词复数时用 those。
I like this pen more than that one. （one代替可数名词单数pen）
There were a few young people and some older ones in the house. （ones代替可数名词复数people）
Mary's handwriting is far better than that of Peter. （that代替不可数名词 handwriting）
These pictures are more beautiful than those. （those代替可数名词复数 pictures）
IV. one既可代替事物, 也可代替人, that只能代替事物而不能代替人。有时可以用the one或the ones代替that或those。
The one ／That on the table is mine. （该句中The one代替事物, 并且也可以用That）
He is the teacher, the one who is loved by the students. （该句中the one代替人, 不能用that）
He advised the farmers to choose the best seed-heads, the ones ／those that had the best color. （该句中the ones代替事物, 并且也可以用those）
V. one一般有前置修饰语, 有时也可有后置修饰语或不用修饰语。而 that不能有前置修饰语, 但可有后置修饰语。
Cook was a strict but good captain, one who took good care of his sailors.
The water in the well is cleaner than that in the river.
VI. it可以替代句中的不定式或从句等, 充当形式主语或形式宾语。one与that均无此用法。
It is known to everybody that the moon travels around the earth once every month.
I found it hard to get on with her.
VII. it与that均可以替代上文全句的内容或部分内容, 而one ／ones则不可以。
He has saved my life; I'll never forget it. （it代替第一分句）
Tom is painting his house. I am told he does it every four years. （it代替前面分句的部分内容painting his house）
Let's say we meet here at three o'clock. That ought to give you。

一、it作人称代词
1. 指代事物。作为人称代词，it 可以指除人以外的一切事物或动物。如：
Sam picked up some knowledge of the computer just by watching others working on it. 山姆只是凭借看别人操作电脑就学到了一些电脑知识。(指the computer) (山东2010)
2. 指代人。主要用于指婴儿或未知的人。如：
I was just going to cut my rose bushes but someone had done it. Was it you? 我正要剪切我的玫瑰丛但(发现)有人已经这样做了。是你干的吗？(未知的人) (湖南 2010)
3. 代替某些代词。代词 it 还可用于代替指示代词this, that 以及复合不定代词 something, anything等。如：
— What’s this / that? 这/那是什么？
— It’s an orange. 这/那是一个橘子。
二、it作非人称代词
1. it用于指时间、距离、价值、自然现象、环境等。如：
It rained heavily in the south, causing serious flooding in several provinces. 南方下了大雨，在几个省造成了严重洪灾。 (指自然现象) (天津 2010)
2. it指代前面提到过的或谈话双方都明白的事情或情况。
三、it作形式主语
当不定式、动名词、从句等用作句子主语时，为保持句子平衡，通常把真正的主语放在句末，而在句首使用形式主语it。
四、it作形式宾语
当不定式、动名词、从句等用作句子的宾语时，通常把它们放在句末，而用it作句子的形式宾语。如：
Mothers holding jobs outside the home should have flexible schedules to make it easier to care for their children. 在外工作的母亲们应该有灵活的时间以便照看她们的孩子。

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! “one”的用法

“one”可以指人，也可以指物。用来代替上文中提到的单数可数名词以及避免重复，其复数形式为ones。One兼有名词和形容词的作用，可以被“this, that, the, another, which”等修饰，可作主语、宾语、表语和定语。“It”是人称代词，可用来指代前面所提到过的某个对象，其复数形式为“them”。

one,it,that的用法区别