Consider the following statements about ultrasonic waves.
1. They can destroy insects.
2. They can clean clothes by removing dust.
3. They can be used to treat diseases.
4. They can control automatic doors.
Of the above statements.

A. Water B. Steel C. Glasss D. Air

A. 20Hertz to 2000 Hertz B. 20Hertz to 200Hertz C. 20 Hertz to 20000 Hertz D. 2 Hertz to 2000 Hertz

A. Frequency B. Wavelength C. Amplitude D. Overtones

A. On land B. In air C. In space D. Underwater