5 1. The weather in Wuhan in summer is hotter than that in Beijing. What is the meaning of this?

C is correct (it replaces uncountable nouns, such as weather and population)

Note: a replaces something similar; B instead of those things mentioned above; D is just a general instruction, and it will not be used to replace anything. such as

Your coat is very beautiful. Where did you buy it? Here, it replaces your coat.

I want to buy one. Replace the same coat as you with one.