The correct answer is Capacitor. A capacitor combined with an inductor makes a resonant circuit (also called a tuned circuit). When an inductor and capacitor are connected together (in series or parallel), they create a circuit that resonates at a specific frequency determined by the values of L and C. This resonance creates a frequency-selective response, making resonant circuits essential for tuning, filtering, and frequency selection. For amateur radio operators, LC resonant circuits are fundamental to antenna tuners, RF filters, oscillators, and receiver tuning. The resonant frequency is calculated as f = 1/(2π√LC), making it a key concept in RF circuit design.