Final answer:
The three key components used in assignment E/M codes are history, examination, and medical decision making.
Step-by-step explanation:
In assignment E/M codes, three key components are used. These components are history, examination, and medical decision making. E/M codes, or evaluation and management codes, are used in medical billing and coding to describe the level of service provided during a patient encounter. The history component focuses on gathering information about the patient's medical background, the examination component involves the physical examination performed by the healthcare provider, and the medical decision-making component refers to the complexity of the clinical decision-making involved in the patient's care.