this和that是单数，these和those都是复数。
these 主要指近物“这些的”.如“these books” 这些书。
例句：
How much money are these books altogether?
这些书一共多少钱？
How much are these eggs?
这些鸡蛋多少钱？
those 主要指远处的“那些的” 如“those books”那些书。
例句：
How much are those blue socks?
那些蓝色的袜子多少钱？
did not know those people who encountered disaster together with me.
我不知道那些与我同时遭遇灾难的人是谁。
