Which statement about closed-loop control under disturbance is true?

• A. It ignores disturbances.
• B. It cannot adjust to disturbances.
• C. It always operates without sensors.
• D. It uses feedback to compensate for disturbances.

Answer: (D)

Closed-loop control uses feedback to reject disturbances. It continuously measures the output with sensors, compares it to the desired reference, and uses the difference (the error) to adjust the input. When a disturbance pushes the output away from the target, the feedback detects the deviation and applies a corrective action to bring the output back toward the setpoint. For example, a thermostat maintains room temperature by sensing actual temperature and increasing or decreasing heating to compensate for disturbances like door opening. The other statements fail because ignoring disturbances prevents compensation, lacking sensors means you can’t detect deviations to correct, and not adjusting to disturbances would leave the system off its target.