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: The Voyage. Sentence 1: Tim was apprehensive about the trip, but still excited. Sentence 2: He boarded the boat. Sentence 3: Tim didn't know exactly what he would encounter. Sentence 4: The boat left the dock and went up the river. Choices: a. They all decided Mary should become part of the family. b. Tim was traveling down the Congo, nervous but excited.
a