A. between 20 hertz and 1000 hertz
B. between 1000 hertz and 20000 hertz
C. less than 20 hertz
D. more than 20 kilohertz
Ultrasonic wave is defined as “inaudible sound with high frequency for human” the frequency of which generally exceeds 20 kHz. These days, sound wave which is not intended to be heard is also called ultrasonic wave.