The correct answer is C: Simplex. Simplex operation means a station is transmitting and receiving on the same frequency. This is the simplest form of two-way communication, where both stations use the same frequency and take turns transmitting and receiving. Simplex is commonly used for direct station-to-station communications without a repeater. On 2 meters, 146.52 MHz is the national simplex calling frequency. Simplex operation is straightforward but has limited range compared to repeater operation. Full duplex allows simultaneous transmission and reception on different frequencies (like telephone conversations), but simplex requires taking turns.