The correct answer is B. closed loop control system.
A closed loop control system is a system that uses feedback to control its output. In the case of an automatic toaster, the input is the desired toastiness of the bread, the output is the toastiness of the bread, and the feedback is the temperature of the bread. The toaster uses the feedback to control the output, in this case by turning off the heating element when the bread reaches the desired temperature.
An open loop control system is a system that does not use feedback to control its output. In the case of an automatic toaster, an open loop control system would simply turn on the heating element for a fixed amount of time, regardless of the temperature of the bread. This would likely result in overcooked or undercooked toast.
A partially closed loop control system is a system that uses some feedback to control its output, but not all of the feedback. In the case of an automatic toaster, a partially closed loop control system might use the temperature of the bread to control the output, but it might not use the desired toastiness of the bread. This would likely result in toast that is not evenly cooked.
In conclusion, an automatic toaster is a closed loop control system because it uses feedback to control its output.