The correct answer is A.
A modem is a device that converts digital signals to analog signals and vice versa. This is necessary for communication between computers and other devices over telephone lines. When a modem is sending data, it first sends a request to send signal, or RTS, to the receiving modem. This signal tells the receiving modem that the sending modem is about to send data and that it should prepare to receive it.
The other options are incorrect.
C. Bearing is a term used in navigation to describe the direction of a point from a reference point.
D. Power supply is a device that provides electrical power to a system.
E. None of the above is the correct answer.