Explanation: An abnormally low input voltage at the transmitter indicates an issue with the power supply or excessive current draw. **Excessive overload (B)** means the transmitter is attempting to draw more current than the power source (like a battery or its internal wiring) can efficiently provide. This increased current causes a larger voltage drop across the internal resistance of the battery, cables, and components (V=IR). This "sag" in voltage means less power is delivered to the transmitter, resulting in a lower terminal voltage. **A partially discharged battery (C)** will inherently have a lower terminal voltage than a fully charged one. As a battery discharges, its chemical potential decreases, directly reducing the voltage it can supply to a load. If the battery voltage is already low, the transmitter's input terminal voltage will also be low. **Reversed polarity (A)** would generally prevent the transmitter from operating at all, or potentially cause damage, rather than resulting in abnormally low voltage *while in operation*. Therefore, both excessive overload and a partially discharged battery are direct causes of abnormally low input power terminal voltage.