Explanation: Keying a simple-oscillator type of emergency transmitter by inserting the key in series with the primary of the high voltage plate transformer (A) is a common and effective method. A simple oscillator requires plate voltage to operate and generate RF energy. Placing the key in series with the transformer's primary effectively acts as an on/off switch for the oscillator's high voltage power supply. When the key is pressed, power flows, the oscillator generates RF, and a signal is transmitted. When released, power is cut, and the oscillation stops. This approach is safe because the key only handles the primary side's AC line voltage, isolating the operator from the hazardous high DC plate voltages and RF energy. Options B and C are incorrect. Inserting the key in parallel with the primary (B) would short out the transformer when closed, causing a massive current surge and likely damaging the power supply. Placing the key in series with the final output to the antenna (C) would expose the operator to high RF voltages and currents, causing arcing at the key contacts, poor signal quality, and potential equipment damage.