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: A pet deck. Sentence 1: Mike and Tony bought a baby duck at the spring festival. Sentence 2: It was decided that Mike was going to keep the duck at night. Sentence 3: Tony came and pick the duck up one morning. Sentence 4: He never returned the duck that night. Choices: a. The doctor said she was not pregnant. b. The next day he told Mike that the duck had died.
b