Well, the whole novel is basically told through these letters, so they are used to advance the plot an offer some sense of authenticity to an implausible story. Plus, it is a way for them to express their own feelings and thoughts about the whole thing.
Answer: talks to other parts of the brain about events related to rewards and any perceived fear.
Explanation:
Most likely A.
In this case a simple statement could be any of those, to shorten to the simple statement you would generalize :)
