00:05Question says, ultrasonic waves are those waves A to which men can hear, B men cannot
00:16hear, C are of high velocity, D of high amplitude, is ultrasonic waves are those having frequency
00:30greater than 20 kilohertz, means 20,000 Hertz, so these waves cannot be detected by human,
00:53so the correct option will be B, men, cont here.
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