Given the task definition and input, reply with output. 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: Baby Sitter. Sentence 1: My nephew recently moved to Stoughton. Sentence 2: He and his wife have a 20 month old boy. Sentence 3: This Saturday, he and his wife had to work. Sentence 4: His mother in Cambridge could baby sit but does not drive on highways. Choices: a. He had to pick her up in Cambridge and bring her to Stoughton. b. After I got home, I sent the stranger a check for $10,000.
a