Which of the following communication modes supports two-way traffic, but in only one direction at a time?

The correct answer is B, Half-duplex. Data can travel between two devices in three modes. In half-duplex mode both devices can send and receive, but only one of them may transmit at any given moment, so the traffic takes turns; a walkie-talkie is the standard example, and older hubs and CB radio worked the same way. In simplex mode data moves in one direction only, as from a keyboard to the computer or from a radio station to a receiver. In full-duplex mode both sides can send and receive at the same time, as in a telephone call or on a modern switched network. A is wrong because simplex allows no return traffic at all. C is wrong because three-quarters duplex is not a recognised mode. D is wrong because only one of the listed modes fits the description. Exam tip: simplex is one way, half-duplex is both ways by turns, full-duplex is both ways together.