Explanation: A Hertz antenna resonates when its inductive and capacitive reactances cancel each other out, making it appear purely resistive. * **B) Placing an inductance in series with the antenna.** Adding an inductor (coil) in series increases the total inductive reactance of the antenna. To restore resonance (where total inductive reactance equals total capacitive reactance), the antenna must operate at a lower frequency. At a lower frequency, the antenna's inherent capacitive reactance increases, bringing the circuit back to balance. This effectively makes the antenna electrically "longer" and thus lowers its resonant frequency. * **A) Lowering the frequency of the transmitter.** This merely means the transmitter is operating off-resonance with the antenna; it does not change the antenna's inherent resonant frequency. * **C) Placing a condenser (capacitor) in series with the antenna.** Adding a capacitor in series increases the total capacitive reactance. To restore resonance, the antenna would need to operate at a higher frequency where its inherent inductive reactance would increase, effectively making it electrically "shorter." This would *raise* the resonant frequency. * **D) Placing a resistor in series with the antenna.** A resistor adds only resistance to the circuit. While it increases losses and broadens the antenna's bandwidth, it does not change the frequency at which the reactive components cancel out (i.e., the resonant frequency).