Definition: 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'.
Input: Sentence 1: One day my wife and I were on the bench in front of our building. Sentence 2: We saw a boy about six years old on a scooter. Sentence 3: The boy rode down the driveway and into the building. Sentence 4: We never saw any adult with the child. Sentence 5: We were amazed and concerned about this. Choices: a. Single Child. b. Puzzle.

a