In my opinion, the correct answer is B. His mystery feeds their imagination. The children have never even seen Boo, so they like to imagine and envision different spooky details about him. Jem fantasizes that he catches and eats squirrels and cats, which is why his hands are always bloody; he drools, his teeth are rotten, he has a dreadful scar on his face, etc.
The correct answer should be A. Exposition.
Expositions are usually located at the beginning of a play and are used to show not only the conflict that is happening, but some other points like the characters and the setting.
10.) A light from the shadows shall spring
Think of some of the highlights and not so great moments of your life. Also try to write it in chronological order from when they took place. I havent lived your life so I cant really give you examples.
