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: Will wanted to go for a hike. Sentence 2: He went into the desert for a bit. Sentence 3: Soon, he came across the border to Mexico. Sentence 4: Will decided he shouldn't cross that border. Sentence 5: He had no choice but to turn back. Choices: a. Introvert Party. b. The Border.

b