A. DC Motor
B. Stepper Motor
C. Relay
D. Shutter doors

Solution

D. Shutter doors

Explanation

<p>An actuator is a device that converts control signals into physical movement or action. Let’s look at each option:</p><ul><li>DC Motor – Actuator (converts electrical energy into rotation).</li><li>Stepper Motor – Actuator (provides precise rotational movement).</li><li>Relay –Actuator (electrically operated switch).</li><li>Shutter doors – Not an actuator themselves, but actuated by motors or other actuators.</li></ul>