it 指代原事原物.如:I bought a pen yesterday,but I lost it.
that 常指代不可数名词.如:The weather in Beijing is colder than that in Shanghai.(that 指代the weather)
this "这个”区别于“那个”,指离说话人更近的一个.
one 指代相同种类的另一个,(区别于it 所指的原事原物).
如:I bought a pen yesterday,but I lost it,so i want to buy a new one.