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: Zach had a very rare blood type. Sentence 2: So when he was diagnosed with bone marrow disease, he was scared. Sentence 3: The chance of finding a donor to help him was slim. Sentence 4: He stayed on a list many months. Sentence 5: But in the end, no match was found and he died. Choices: a. Rare blood type. b. Health Evolution.

a