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: It's Green. Sentence 1: Trouble brewing at the Olympic games. Sentence 2: Water in several pools has turned green. Sentence 3: There are now two pools that have bright green water. Sentence 4: The water is supposed to be azure in color. Choices: a. I drove on the highway and everything turned out fine. b. Olympic officials are trying to find out the cause.
b