The correct answer is A) only one person may talk at a time. VHF marine band radios operate in simplex mode, which means that only one person can talk at a time. In simplex mode, the radio uses the same frequency for both transmitting and receiving, and the radio can only do one or the other at a given time. This allows for clear communication, as the radio cannot transmit and receive simultaneously, ensuring that only one person is speaking at a time. The other options are incorrect because: B) is incorrect as simplex mode allows only one person to talk at a time, not two; C) is incorrect as the radio can both transmit and receive in simplex mode; and D) is incorrect as the radio can both transmit and receive in simplex mode, not just receive.