무엇에 대한 이야기인지 고르십시오 means “choose what the story is about”.
In this item you are going to find the main idea.
Reread the First and Last Sentence –
After reading, read again the first and last sentences. It’s safe to say that the author will indicate the main idea in either the first few lines of text or the last few lines. As part of a conclusion, many writers will emphasize the main idea by mentioning it several times.
Look for Repeated Ideas – there will be some central concept that the author keeps going back to. These are repeated ideas.