Which of the following is a closed-loop control system?

(a) Traffic control on the roads by lights where the timing mechanism is present irrespective of the intensity of traffic

(b) Switching off the street lights of a tower at a predetermined time by a time-switch irrespective of the fact that the sun rises at a different time each day

(c) Switching off an electric heater by a time-switch irrespective of whether the dish has been prepared or not

(d) Human body.