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Indicate Time

For example, 晚上(at night), 早上(in the morning), 课上(during a class)

课上老师讲的，你听懂了吗？
Did you understand what the teacher said in class.

会议上我们什么也没讨论。 We didn’t discuss anything at the meeting

= on a surface.

For example, 桌上(on a table), 书上(in a book), 墙上(on a wall).

我会这本书上所有的字。
= 我会这本书里所有的字。(里 is acceptble as well)
I know all the words in this book.

墙上有一个洞。
There is a hole in the wall.

墙上有一幅画。
There is a picture on the wall

= within a scope, regarding an aspect.

For example, 文化上(regards to culture), 历史上(in history), 性格上(regards to personality).

每个国家都有文化上的特色。
= Every country has cultural characteristics. (has characteristics in culture)

我知道很多历史上的名人。
= I know many famous people in history.

他性格上很不错。 = He is very good in character. (in terms of personality, he’s good.)