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 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: The Black Dog. Sentence 1: The dog was barking at the front door. Sentence 2: James wondered if someone was standing outside of it. Sentence 3: He snuck to the window and looked. Sentence 4: The porch was empty. Choices: a. The dog just liked to bark at nothing. b. Bob was very relieved he didn't have to replace the whole heater.
a