The line that states, "courage is a man with a gun in his hand." It is a metaphor because Lee is not comparing courage to a man with a gun with "like" or "as." Instead, she uses "is", as if she is enforcing the fact that courage IS a man with a gun. That kind of bluntness is only in a metaphor, as the author gives no room for debate.
"David throws" is the one among the following choices given in the question that is the independent clause. The correct option among all the options that are given in the question is the second option or option "B". An independent clause always has a subject and a predicate. I hope the answer has helped you.
The question suggests that there are a number of possible answers to choose from. You haven't shown those, but I would take a wild guess and say, possibly, being bullied as a child?