The correct answer is C: Potentiometer. A potentiometer is the type of component often used as an adjustable volume control. Potentiometers are variable resistors with three terminals that allow you to adjust resistance, making them ideal for volume controls. Potentiometers (pots) are variable resistors with a rotating or sliding contact that moves along a resistive element. They have three terminals: two end terminals and a wiper (center terminal). As you turn the knob, the wiper moves, changing the resistance between the wiper and each end terminal. This makes them perfect for volume controls, tone controls, and any application where you need to adjust a signal level. They're commonly found in audio equipment, radios, and test instruments.