The correct answer is B) low or zero voltage drop reading, while the other coils will have higher readings. When testing the rotor of a synchronous motor for short circuits, a low voltage source is applied across the rotor coils through the collector rings. If a coil is short-circuited, it will create a low or zero voltage drop across that coil, while the other healthy coils will have higher voltage drop readings. This is because the short-circuited coil effectively becomes a low-resistance path, resulting in a lower voltage drop compared to the non-shorted coils. The other options are incorrect because: A) a high voltage drop would indicate an open circuit, not a short circuit; C) a steady voltmeter reading would not be the expected behavior for a short-circuited coil; and D) a fluctuating voltmeter reading is more likely to indicate an intermittent issue, not a clear short-circuit indication.