that 是不同地方的 it 是相同地方的 例:beijing'weather is more cold than that in shanghai 你看 北京和上海是两个不同的城市 所以用that 再举一个例子 today'weather is more cold than it yesterday 因为是同一个地方的两天的天气 所以用it that就是引导宾语从句的先行词
this”、“that”既可以作形容词,又可以作指示代词；而“it”只能作代词.one可用数词又可作代词.
指“物”
1.“this”指近物,“that”指远物,“it”没有远近之分.如：
This is a computer.这是一台电脑.（在近处）
That is a bike.那是一辆自行车.（在远处）
2.在回答“this”和“that”作主语的疑问句时,常用“it”代替“this”和“that”.如：
－Is this/that a car?这/那是一辆小汽车吗?
－Yes,it is./No,it isn′t.是的,它是./不,它不是.
－What′s this/that?这/那是什么?
－It′s a ruler.这/那是一把尺子.
3.陈述在一起的两样东西时,应先说“this”,后说“that”.如：
This is a book.That is a pen.这是一本书,那是一枝钢笔.
4.one与it的区别
one指代上文提到过的同类事物中的一个,但不是上文提到的那一个事物.如果指同类事物中的一些,要用ones.如：
This apple is small.Please give me a big one.
这个苹果小,请给我一个大的.
These books are mine.Those ones are Lily's.
这些书是我的,那些书是莉莉的.
it指代前文中提到过的那一个事物.如：
My bike is very old,but I like it very much.
我的自行车很旧,但我很喜欢它.
Where is my new pen?I can't find it.
我的新钢笔在哪儿?我找不到它了.
it的用法
1、it指代上文所提事物的本身（it表时间、强调等的用法此处不阐明）,如果所代替的事物为复数,则应该用they或them表示.
2、it也可以用来代替上文所提到的一件事.
1.The Parkers bought a new house but _____ will need a lot of work before they can move in.(NMET2001,25)
A.they B.it C.one D.which
2.I am looking for a house.I’d like ____ with a brook around_____.
A.one,it B.it,it C.one,one D.it,one
3.Mary’s mother always told her to work hard,but______didn’t help.
A.one B.he C.she D.it
4.—Do you like these photos?— Yes,____are very beautiful and I like____ very much.
A.they,those B.they,them C.ones,ones D.the ones,the ones
5.—Are you still using your old car?--No,I sold___the other day.
A.it B.one C.that one D.the one
6.Yesterday I lost my pen,but now I have found_____.
A.it B.them C.ones D.those
7.—Where are my books?--_____ are on the TV set.
A.Ones B.Those C.The ones D.They
8.Where have you put my shoes?I can’t find_____anywhere.
A.them B.those C.ones D.the ones
9.Where did you buy the watch?Would you please get____ for me?
A.it B.one C.the one D.them
10.Don’t read in the sun.____ is bad for your eyes.
A.One B.The one C.It D.This
二、that的用法
1、that用来指前文中确定的非同一事物,常用来替代与定冠词或形容词性物主代词连用的单数可数名词或不可数名词,相当于“the+名词”,其复数形式为those.
2、that表替代时为始终是特指（作指示代词和关系代词用时另论）,可指上文谈到的人、物或情况（均为单数）,可代替可数名词和不可数名词.
3、若that所代替的内容为前置用法,即要代替的内容将出现在下文中,一般用this,these或the following表示.
1.—He was nearly drowned once
—When was_______?(NMET2002 Beijing spring)
—_____was in 1998 when he was in middle school.
A.that,It B.this,This C.this,It D.that,This
2.Equipped with modern facilities,today’s libraries differ from______ (2003 Shanghai spring,26)
A.those of the past B.the past C.which of the past D.those past
3.Few pleasure can equal __of a cool drink on a hot day.(NMET99,17; NMET99 Guangdong,29)
A.some B,any C.that D.those
4.The population of Sichuan Province is larger than ____of any province in China.
A.one B.it C.that D.the one
5.What I want to suggest is_____:Everyone should have another try.We needn’t only wait for help.
A.that B.this C.it D.one
6.You see,the accident happened like_____:The red car hit the bus and made all the traffic stop.
A.that B.this C.it D.one
7.Listen!________ is about the lessons we will have to finish today.
A.It B.The one C.The following D.One
8.The climate here is quite different from____ of Shengyang.
A.that B.it C.one D.the one
9.The study of idioms is as important as____ of grammar.
A.one B.that B.it D.this
10.My seat is next to_____ of my teacher.
A.that B.it C.this D.one