which of these events is an example of the doppler shift? the amplitude of a wave on a string increases as the frequency decreases. the amplitude of sound from a tuning fork decreases due to damping. the frequency of light from a star increases as it moves toward us. the intensity of an electromagnetic wave increases with the field strength. the velocity of an electromagnetic wave changes as its medium changes.

Choice-C (the 3rd one on the list) is sorta kinda on the right track, and it's
the answer that the question is fishing for, but it has a glaring error.

An example of the Doppler shift:

If a star is moving toward us, then the frequency of the light we see
from the star appears higher than it was when it left the star. 

The frequency of the light does NOT "increase as the star moves toward us".

It's constant and it doesn't change.  It just appears higher than it should be.

The whole trick to this kind of observation is this:  When we receive light from
a star and measure its frequency, HOW do we know what it SHOULD BE ? ! ?

The answer is a 0.64 volts