In this task, you're given the title of a five-sentence story, the first four sentences, and two options for the fifth sentence as a and b. Your job is to pick the sentence option that seamlessly connects with the rest of the story, indicating your choice as 'a' or 'b'. If both sentences are plausible, pick the one that makes more sense.

Title: Five hundred thanks. Sentence 1: Alvin was a mechanic driving home during rush hour traffic. Sentence 2: A man was stranded on the side of the road with car troubles. Sentence 3: Alvin pulled over and fixed the man's car in less than an hour. Sentence 4: The stranger told Alvin he was the first person to stop and help. Choices: a. Sissy then had to go to the next one. b. He wrote Alvin a check for five hundred dollar.
b