You will be given a definition of a task first, then some input of the task.
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 seamlessly connects with the rest of the story, indicating your choice as 'a' or 'b'. If both sentences are plausible, pick the one that makes more sense.

Title: Tsunami Sirens. Sentence 1: Bob heard the emergency sirens. Sentence 2: The sirens indicated a tsunami might be headed for his coastal city. Sentence 3: He was driving, so he stayed in his car and headed to higher ground. Sentence 4: He drove several miles inland. Choices: a. A trip to the vet's office revealed a herniated disc. b. Bob then heard the sirens indicating that the danger had passed.
Output:
b