The answer is D. Mitty would rather dream than attend to errands. He's not literally shooting a pistol, so B and C are not the answer. A. can't really be proved with this passage, also he specifies what biscuit he wants.
Answer: D
Explanation: The white people were gonna hunt them down and kill for trying to escape
I think B and also what diagram?
The answer is the last one, D. All of the other transitions indicate that the writer will either go into further detail on the subject or list other reasons as to why this would be correct. However, D clearly uses a contrasting transition to introduce a new argument.