that,those代指在前文中出现的对等的部分(不是同一个事物,只是对等),that指代可数名词单数及不可数名词,those指代可数名词复数
如:The weather in Beijing is colder than that in Kunming.
The apples in red basket are not as sweet as those in black basket.
而it指前文提到的事物,是同一物
如:My pen was lost ,did you see it?
it 是指代离主体比较近的情况,that 是指比较远的情况。
看例,The is my pen. It is in red. 这是我的笔,它是红色的。说话时,笔就在你眼前。
但如说话时,东西离你较远,你要对第三者特意指出来作说明,就要用that.例如,
Where is your seat?
That is my seat.
说话时指著那座位