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: Nina caught a turtle at the pond. Sentence 2: She brought it home to be her pet turtle. Sentence 3: But then her brother taught her about turtles. Sentence 4: Nina decided to set her turtle free. Sentence 5: She didn't want to be a cruel captor! Choices: a. Math Exam. b. Turtle.
b