You will be given a definition of a task first, then some input of the task.
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: Heather loved to tease Fiona. Sentence 2: She hid her things behind the sofa every time she came to see her. Sentence 3: Fiona was really tired of that behavior and retaliated. Sentence 4: She took some of Heather's things and hid them in her purse. Sentence 5: Heather, mollified, promised to stop and their friendship survived. Choices: a. Teasing friends. b. Thriller.
Output:
a