In this task, you're given five sentences, numbered 1 through 5, and two options a and b for possible titles for the story. Your job is to choose the title that better fits the story. Indicate your choice by 'a' or 'b'.
Example: Sentence 1: Marcus needed clothing for a business casual event. Sentence 2: All of his clothes were either too formal or too casual. Sentence 3: He decided to buy a pair of khakis. Sentence 4: The pair he bought fit him perfectly. Sentence 5: Marcus was happy to have the right clothes for the event. Choices: a. Marcus Buys Khakis. b. Marcus Works.
Example solution: a
Example explanation: Marcus's reasons for buying khakis is established, followed by his purchase of them and reaction.

Problem: Sentence 1: My 99 year old friend Ben sits on the bench a lot. Sentence 2: Yesterday he told me he had enrolled in some courses. Sentence 3: Brandeis has courses open for senior citizens. Sentence 4: I asked him why he wanted to go to so many courses. Sentence 5: He said if he keeps busy he won't die. Choices: a. Classes. b. Guilty.
Solution: a