The Doppler effect describes the way the movement of a source or an observer changes
the perceived wavelength and frequency of a wave generated by the source. When the source is
moving toward the observer, the received wavelength is _________ than the generated one, and
when the observer is moving toward the source, the received wavelength is __________ .
A. shorter, shorter
B. shorter, longer
C. longer, shorter
D. longer, longer