Answer:
the second and third are correct!
Step-by-step explanation:
"Main ideas tell you who or what he author is talking about" is true because the main idea helps you support the claim, the whole idea of the author's story.
"Main ideas are found within the most important statement in the paragraph" is also correct because in order to have a important statement, it's best to back it up with a main idea, which is what the statement is about.
hope i helped, tell me if you got it right! :)