Why is the change in sound made by a passing train's whistle similar to the reason the pitch rises quickly in systole and drops quickly in early diastole when measuring arterial sounds?
A)Both are explained by B-mode ultrasonography.
B)Both involve the science of plethysmography.
C)Both are explained by the Doppler effect.
D)Both are explained by the science of atomic behavior in a strong magnetic field such as MRI.