Your old bike is white, while my old one is black.

3.one在定语从句中作先行词替代特指的同一类人或事物时,其前面必须用定冠词the限定,但不可用that替换.如果先行词为"one of...",其关系代词在定语从句中作主语,从句中的谓语动词常用复数形式.例如:

1)This farm is the one that we visited last summer.(句中the one代替this farm,作先行词,不可用that替代)

2)This is one of the highest buildings that have been built in our city recently.

3)Zhang Lei is the very one of the students who has been praised at the meeting.

4.one的复数形式为ones,作替代词时,只可替代同一类人或事物的复数名词,其前面必须有限定词,如the, some, all等修饰.但不能用数词或many修饰.例如:

1)Mr. Zhang gave the textbooks to the pupils except the ones who had already taken them.(句中the ones可用those替代)

2)I don't want to buy these small pears; I want some large ones.

3)She wants to buy some new clothes and throw away all her old ones.

5.one在句中不可替代不可数名词.在句中如果出现了同一个不可数名词时,则需要重复前一个名词,或者省略那个名词.例如:

1)I prefer black coffee to white (coffee) .(white coffee中的coffee可省略也可不省,但不可用one替代coffee)

2)Folk music is the music that I like most.(不可用the one替代the music)

it作代词如何使用：

1.it用来替代前面提到的同一事物时,被替代的名词可以是可数名词,也可以是不可数名词.例如:

1)We are studying in a school with trees all around it.(it替代可数名词school)

2)-Have you still kept your old furniture?

-No,I have sold it.(it替代不可数名词furniture)

2.it可以替代英语句式中的不定式(短语)、动名词(短语)或从句,在句中作形式主语或形式宾语.例如:

1)It is a great surprise to meet you here.(It替代不定式短语to meet you here)

2)I think it is no good parents doing anything for their children.(it替代动名词的复合结构parents doing anything for短语)

3)We found it impossible