<prompt> Doppler effect results from change in -Amplitude of soundFrequency of soundDirection of soundNone of the above  <response>: Doppler effect is due to shift in sound frequency as the sound as reflected from the moving Red blood cells. If the motion of RBC is towards the transducer, the returning sound wave has higher frequency than transmitted wave. If the motion of RBC is away the transducer, the returning sound wave has lower frequency than transmitted wave. Color intenstiy indicates the relative velocity of the red blood cells. 