Which of the following statement is correct?

• A. Satellite transponders contain a device that echos the radiation without change from one point on earth to another
• B. Satellite transponders contain a receiver and transmitter designed to relay microwave transmissions from one point on earth to another
• C. Satellite transponders use lower frequency reception of radiation from earth stations and higher frequency for transmission to earth stations
• D. Satellite transponder contains devices that transform the message sent from one location on earth to a different code for transmission to another location