Which transmission method allows two-way communication with both directions active at the same time?

• A. One way
• B. Two ways at any time
• C. Two way, but only one at a time
• D. Two ways at any time (phone)

Answer: (D)

Two-way communication with both directions active at the same time is full-duplex. In full-duplex systems, you can send and receive simultaneously, so conversations happen in real time without waiting for the other person to finish. A telephone line is a classic example: you can talk and hear each other at the same moment. This contrasts with simplex, where communication is one-way only, and half-duplex, where two-way communication is possible but not at the same time—you have to take turns. The option describing simultaneous two-way communication, such as on a phone line, best fits full-duplex behavior.