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: Over Whitened Teeth. Sentence 1: Ethan always took great care of his teeth. Sentence 2: He made sure to brush and floss as much as possible. Sentence 3: He felt that his teeth were not white enough. Sentence 4: He went to the dentist and got them whitened. Choices: a. Ethan couldn't smile after because his teeth had gotten too white. b. Dave and her wife's family surprised her and she was ecstatic.

a