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: Salt Water. Sentence 1: Ari's saltwater fish tank was struggling. Sentence 2: His fish appeared sick and struggling. Sentence 3: Ari reluctantly put the tank up for sale. Sentence 4: Soon an experienced buyer took the fish off Ari's hands. Choices: a. The buyer cared for Ari's fish and made them healthy again. b. They didn't get an answer, because the bear broke through the door.
a