Final answer:
The correct answer is Diagnosis code. The diagnosis code serves as an index to a patient's medical history.
Step-by-step explanation:
The correct answer is B) Diagnosis code.
The diagnosis code serves as an index to a patient's medical history. It provides a standardized way to encode specific medical diagnoses and major medical disorders experienced by a patient.
For example, if a patient has been diagnosed with diabetes, the corresponding diagnosis code would indicate this condition in the patient's medical history.