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: Bike Rides. Sentence 1: Hillary learned to ride a bike yesterday. Sentence 2: I was worried that she would fall, but her big brother was careful. Sentence 3: He ran next to her bike while she pedaled. Sentence 4: Soon, she was riding in circles! Choices: a. Her brother got his bike out and they rode around together. b. The distance made them grow apart and they broke up.
a