The correct answer is A. Closed loop system.
A closed-loop system is a control system in which the output is measured and compared to a desired value, and the difference is used to adjust the input to the system. This feedback loop allows the system to correct for disturbances and maintain a desired output.
An open-loop system is a control system in which the output is not measured and compared to a desired value. The input to the system is determined solely by the desired output. Open-loop systems are less stable than closed-loop systems and are more susceptible to disturbances.
A semi-closed loop system is a control system that combines elements of both open-loop and closed-loop systems. The output is measured and compared to a desired value, but the difference is not used to adjust the input to the system. Semi-closed loop systems are more stable than open-loop systems, but less stable than closed-loop systems.
In conclusion, a closed-loop system is a control system in which the output is measured and compared to a desired value, and the difference is used to adjust the input to the system. This feedback loop allows the system to correct for disturbances and maintain a desired output.