Explanation: The observation that all filaments are burning and plate and grid meters read normal currents and voltages indicates that the master oscillator and power amplifier stages are functioning correctly and generating RF power. The issue is therefore with the measurement of antenna current, not the generation of power. A **shorted antenna ammeter** (A) would provide a low-resistance path for the RF current, bypassing the meter's internal sensing element. The RF power would still reach the antenna (or at least proceed past the meter), but the ammeter would show zero because no current is flowing *through its measuring coil*. An **open connection in the remote reading meter** (B) would interrupt the circuit that provides the signal to the meter, causing it to read zero. For example, in a thermocouple ammeter system, an open in the DC meter line would mean the meter sees no voltage, even if the thermocouple at the antenna feed point is still converting RF to heat. The RF power would still be transmitted to the antenna, unaffected by the remote meter's circuit integrity. Since both scenarios result in the antenna ammeter reading zero while the transmitter itself is operating normally (as indicated by normal plate and grid currents/voltages), both A and B are plausible explanations. Therefore, C is the correct answer.