In duplex operation, what problem does it address?

Duplex operation addresses the issue of communication by allowing simultaneous two-way transmissions, enhancing overall efficiency in conversation. Unlike simplex communication, where information flows in only one direction (from sender to receiver), duplex systems enable both parties to transmit messages at the same time. This characteristic effectively addresses problems arising from obstructions that may interfere with the linear flow of information, as duplex systems can circumvent delays and interruptions typically seen in simplex communication setups.

In contrast, the other options focus on aspects that are not directly related to the fundamental purpose of duplex operation. Reducing communication costs may be a benefit in some scenarios, but it is not a core function of duplex systems. Similarly, limiting the number of users on a channel or improving clarity of communication does not capture the essence of how duplex operation functions as it primarily facilitates two-way communication rather than simply enhancing clarity or user capacity. Thus, the correct answer highlights the critical role duplex operation plays in improving communication systems by addressing limitations inherent in simplex communication.