Question

The two kinds of sounds that we cannot hear are __________ and __________.

• A. infrasonic,sonic
  
• B. sonic,infrasonic
• C. ultrasonic,infrasonic
• D. ultrasonic, sonic

Answer 1

The correct option is C ultrasonic,infrasonic

Normal human hearing range is from 20Hz to 20kHz and sounds within this frequency range are called sonic sounds. A sound with frequency less than 20 Hz is called infrasonic sound and a sound with a frequency above 20kHz is called ultrasonic sound.
Infrasonic and ultrasonic sounds are not audible to us.