Technician exam question T2A11

WhySimplex describes an amateur station transmitting and receiving on the same frequency. Simplex describes a station transmitting and receiving on the same single frequency, the way two stations talk directly to each other without a repeater, answer C. Full duplex (A) means transmitting and receiving simultaneously on two different frequencies, like a phone call, diplex (B) and multiplex (D) both refer to combining multiple signals or channels, not to same-frequency operation.