Answer:
D) feedback.
Step-by-step explanation:
An air condtioning unit consists of the following elements according to available choices:
Inputs: Refrigerant, air from surroundings, electricity.
Process: Refrigeration cycle.
Output: Conditioned air at goal temperature.
Feedback: Activation and deactivation of the air conditioning unit depending on indoor temperature.
When the air conditioning turns on and off to keep goal temperature indoors, a control stage consisting in a controller and a action element is acting to reverse the behavior of the process with a view to keep goal temperature.
Hence, correct answer is D.