How are radar and an approaching siren alike? How are they different?
A. Both use sound waves, but the Doppler effect can be observed
only with radar.
B. Both use sound waves, but the Doppler effect can be observed
only in the approaching siren.
C. Both exhibit the Doppler effect, but radar uses radio, and the siren
'uses sound waves.
D. Both exhibit the Doppler effect, but radar uses sound waves, and
the siren uses radio.
