The line itself is saying that killing someone will make sure they can't hurt you, since dead men don't bite. That makes Billy's character seem like he led a rough life which is what I would answer with. He is not jovial, because that means cheerful, and the line doesn't give indication that all of Billy's friends are dead or that he doesn't like to think of the future, so I'd say answer A.
The prepositional phrase " on the park bench " acts as an adjective phrase....it is describing the man...it is answering the question " which man "...the one on the park bench.
B because he knows he can see something when he is almost home