A simple lecture is a class. In America, the average teacher says how long it takes to finish this part is all in class. For example, I have to take a subject several times, that is, I will take classes after a few classes.

SECTIon is used in some parts of the course, such as a subject. I need to use section to complete it in several parts.

Unit has never seen anyone use it, and it is only a single question.