The best answer would be Letter B - to entertain.
The author merely would like to provide amusement to the readers at his expense. It certainly does not persuade, explain, nor inform anything since it states - <span>But why bother with the descriptions; you’ve probably already grasped the idea!</span> - which could be taken as a witticism.
I am pretty sure it would be massive because it is an English question. If you are doing a multiple choice question you should see which one fits the best. If could also be positive impact.
Answer:
She is not writing a letter.