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 does not connect with the rest of the story, indicating your choice as 'a' or 'b'. If both sentences are plausible, pick the one that makes less sense.

Title: Corina's New Brushes. Sentence 1: Corina enjoyed painting. Sentence 2: She needed a new set of paintbrushes. Sentence 3: Corina's birthday was coming up. Sentence 4: For her birthday, her parents bought her a new set of brushes. Choices: a. Mike had a great time on his vacation. b. Corina was excited to use her new brushes.
a