What role does a capacitor play in AC circuits?

In AC circuits, a capacitor is essential as it stores and releases electrical energy. This functionality arises from the capacitor's ability to charge and discharge, which allows it to temporarily hold electrical energy in an electric field.

When connected to an AC circuit, the alternating current causes the voltage across the capacitor to change continuously, leading to the capacitor charging and discharging in sync with the AC voltage fluctuations. This energy storage capability contributes to power factor correction, filtering, and smoothing of signals, which enhances the overall performance of the circuit.

The roles of the other options do not accurately reflect the primary function of a capacitor in AC circuits. While there are components and mechanisms that perform tasks like connecting circuits in parallel or measuring voltage levels, these are not functions of a capacitor. Instead, the core characteristic of a capacitor is its ability to store and release electrical energy, making this the correct answer.