Given the task definition and input, reply with output. 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'.

Sentence 1: Billy's parents bought him a bike without training wheels. Sentence 2: Billy didn't know how to ride a bike yet. Sentence 3: Billy's dad would hold the bike and walk while Billy rode it. Sentence 4: Eventually, Billy's dad was able to let go of the bike. Sentence 5: Billy kept riding his bike. Choices: a. Learning How To Ride A Bike. b. Foggy Weather.
a