Question

Which of these events is an example of the Doppler shift?
A)The amplitude of a wave on a string increases as the frequency decreases.
B)The amplitude of sound from a tuning fork decreases due to damping.
C)The frequency of light from a star increases as it moves toward us.
D)The intensity of an electromagnetic wave increases with the field strength
E)The velocity of an electromagnetic wave changes as its medium changes.