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: Joan decided to throw a Halloween party. Sentence 2: She thought of many great costumes, but couldn't decide which to wear. Sentence 3: She decided to be a witch. Sentence 4: She picked her costume carefully. Sentence 5: At the party, someone else was wearing the exact same costume. Choices: a. Halloween. b. The Chalk.

a