区别one,the one,it,that,

one：一个或某人的意思,除了做数量词外常用于列举（常有其中一个的意思）
eg：There are two bags on the table,one is white,the other is blue.
当前面有定冠词the 的时候,the one 就有了“特定”的意思
eg：There are two bags on the table,mine is the red one；为了方便比较,看成mine is the one that is red.就行了
it：“它”,指代事物,常作独立的个体,可以另起句子.可比较one 与it区别如下：
eg：There are two bags on the table,one of which is mine.It is red.
that：“那个”,可以用来接从句,作名词时也可指代事物.要分这个不困难,牢记它的中文意思,代入感觉是否通顺.
eg：如果把上一句的it改that就会很奇怪：那个是红色的.（它是红色的就可以了）
that指代常有特定句型（比较级之类）The weather in Shanghai is warmer than that in Beijing.
ps：参考自百科