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: Tom heard rumbling in his home. Sentence 2: He followed the sound around the house. Sentence 3: He determined it was mice. Sentence 4: He set up mouse traps. Sentence 5: He killed the mice and no longer heard mice in his home. Choices: a. Mouse. b. Spitball.
a