Given the task definition and input, reply with output. In this task, you're given the title of a five-sentence story, the first four sentences, and two options for the fifth sentence as a and b. Your job is to pick the sentence option that does not connect with the rest of the story, indicating your choice as 'a' or 'b'. If both sentences are plausible, pick the one that makes less sense.

Title: Thirst. Sentence 1: Joe just finished running a mile. Sentence 2: And he really needed something to drink. Sentence 3: He headed towards the nearest water fountain. Sentence 4: But the water tasted odd and barely helped his thirst. Choices: a. It had been a very scary day for them. b. When he got home, he felt very weak and sick.
a