Which best explains the children's fascination with Boo Radley? They pity him. His mystery feeds their imagination. They are determined to draw him out. He is an easy target for their pranks.

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.