Cell phones depend on both mechanical and electromagnetic waves to be useful. which answer below correctly identifies how each wave is used in cell phones?

a. mechanical waves allow the buttons to be pressed to make a call; electromagnetic waves allow a signal to be picked up when making a call

b. mechanical waves light up the screen; electromagnetic waves create the sound when the phone is ringing

c. mechanical waves allow the cell phone to emit a sound when ringing; electromagnetic waves allow a signal to be picked up when making a call.

d. mechanical waves allow a signal to be picked up when making a call; electromagnetic waves allow the cell phone to emit a sound when ringing