We can only tell the earth is rotating almost 960 miles an hour if we a
look at other people around us as a reference point.

b
look at mountains far away from us as a reference point.

c
use a reference that is not on the earth, like the sun or stars.

C

It is C i have to type this because i need 20 characters.

sonar - device which is used to find the submit submarines, sankalp ship. sonar waves consists of a transmitter and detector which are installed in the observation centre on board of a ship. the ultrasonic waves are sent into the sea at high frequency about 1000 khz in all direction.