D. none of these
Ships use echo to find the depth of the water beneath them.
Depth finder, also called echo sounder, a device used on ships to determine the depth of water by measuring the time it takes a sound (sonic pulse) produced just below the water surface to return, or echo, from the bottom of the body of water.
Formula to calculate depth of sea
Use the following Formula to calculate depth of sea
D = V Times 1/2 T
D = Depth (in meters)
T= Time (in seconds)
V = 1507 m/s (speed of sound in water)