You are standing on a street corner and you hear an ambulance siren. the pitch of the siren seems to be getting higher. what do you expect will happen next? a. the pitch of the siren will change unpredictably as it approaches you. b. the siren will get louder and higher as the ambulance moves towards you. c. the siren will eventually fade as the ambulance moves away from you. d. the pitch of the siren will continue to get higher, but you will not see the ambulance because it is moving away.