Though it's not impossible, you will almost NEVER see exposition anywhere except the beginning of the story. The definition of exposition is "setting up the world of the story", so the answer is the only option that sets up the story. Every other answer happens after the world has already been set up, so they cannot be the exposition
"Politeness is half good manners and half good lying" because when someone asks you how you are, you politely reply 'I'm doing good/well' even if your not - a lie. :)
