The reason that a police car's siren sounds HIGHER in pitch as it approaches you, is because the truck pushes the sound waves together so that the sound wavelengths in front of the truck gets shorter. This causes the
A
Frequency to increase, which increases the pitch
B
Velocity to decrease, which increases the frequency
C
Frequency to decrease, which decreases the pitch
D
Wavelengths to get longer, which increases the pitch