What does duplex mean?

• A. One-way communication
• B. No communication
• C. Simultaneous talk-listen communications
• D. Frequency multiplexing

Answer: (C)

Duplex means two-way communication. In duplex systems you can both send and receive signals. When both directions occur at the same time, that’s full duplex—often described as simultaneous talk-listen. If two-way communication happens but not at the same time, it’s half duplex; if there is only one direction, it’s simplex. The option describing simultaneous talk-listen communications matches the idea of duplex in common usage, such as a telephone call where you can speak and listen at the same time. The other choices refer to one-way transmission, no transmission, or a separate technique (multiplexing) that isn’t about the directionality of the conversation.