Question

Ultrasonic waves _____.

-are painful to the human ear
-are sound waves with frequencies below 20 Hz
-can be used to see internal organs
-travel most quickly through gases

Answer 1

HEY mate !! HERE is your answer !!

I think the option C is correct-can be used to see internal organs.

Hope it helps you.

good night

^_^

Answer 2

Here is your answer ultrasonic waves are painful to the human ear.

....Hope it helps!