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: Mark had a dog who he loved with all his heart. Sentence 2: He fed him daily and had no idea that the dog was vicious. Sentence 3: He found out one day when he got home and the police were there. Sentence 4: His dog had attacked five children and had to be put down. Sentence 5: Mark took the dog to the pound and they immediately put him to sleep. Choices: a. The Vicious Dog. b. Locked out.
Output:
a