The correct answer is: A. Switches.
Enhancement-mode MOSFETs are a type of transistor that can be used as a switch. They are turned on when a voltage is applied to the gate, and turned off when the gate is left open. This makes them ideal for use in digital circuits, where they can be used to create logic gates and flip-flops.
Resisters are used to control the flow of current in a circuit. They are made of materials that have a high resistance to the flow of electrons. This resistance can be used to create voltage drops, which can be used to control the operation of other components in a circuit.
Capacitors are used to store electrical charge. They are made of two conductive plates separated by an insulator. When a voltage is applied to the capacitor, the charge will accumulate on the plates. This charge can then be used to power other components in a circuit.
Buffers are used to isolate two circuits from each other. They do this by amplifying the signal from one circuit and then passing it on to the other circuit. This prevents the two circuits from interfering with each other.