You will be given a definition of a task first, then some input of the task.
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: Sibling Rivalry. Sentence 1: Dan and his brother Don have always been competitive. Sentence 2: Recently there was a marathon occurring in Boston. Sentence 3: Dan and Don decided to see who could get the better time. Sentence 4: However, during the marathon, Don fell and could not finish the race. Choices: a. Dan decided to help his brother instead of finishing the race. b. Dan was angry that his neighbor was so darn nosy.
Output:
a