Answer:
The bottom two are correctly used, the top 2 are not.
Explanation:
A colon is correctly used for a list of items or normal nouns. However the top two are naming an order of events and a order of what needs to be found. This is not used for a colon since there used for a list not a period of time. The next part of the explanation is the bottom two use a list for things needed for a ballet school, and a list of things that make smog. That's the proper use for a colon.
