400
"Gabriel is standing on a street corner as an ambulance approaches. As the ambulance gets closer, the pitch of the sound waves is higher. Then, as the ambulance passes and moves father away, the pitch decreases. Based on this imformation, what do the sound waves from the siren have when the ambulance is being driven toward Gabriel?"
A) The same frequency
B) A higher frequency
C) A decreasing frequency
D) A lower frequency
What is B) A higher frequecy