The correct answer is: A. current
A capacitor is a circuit component that stores electrical energy in an electric field. It does this by opposing changes in the current flowing through it. When current flows into a capacitor, it charges the plates of the capacitor. When the current stops flowing, the capacitor discharges, releasing the stored energy.
Capacitors are used in a variety of electronic circuits, including filters, amplifiers, and oscillators. They are also used in power supplies to smooth out the output voltage.
Option B is incorrect because voltage is the difference in electrical potential between two points. It is not a circuit component.
Option C is incorrect because impedance is the total opposition to current flow in an electric circuit. It is a combination of resistance, capacitance, and inductance.
Option D is incorrect because capacitors do oppose changes in current.