Answer: The correct answer is microwave.
Explanation:
Microwave is an electromagnetic wave. It does not need any medium to travel. It travels with the speed of light through vacuum.
The microwave is used to send information from the cell. It may be text message, conversation or video clip.
The cell receives microwave signal from the transmitter and sends microwave signal back.
Radar wave is used in detection system. It uses the radio wave to measure velocity of the object and velocity of the object.
Therefore, the answer is microwave.
