He had three discrete symptoms, causing the doctor to create an elaborate plan of care.

The correct answer is A: Individual. In this context, "discrete" means separate or distinct. Therefore, the symptoms were distinct and separate from each other, indicating that they were individual symptoms. "Difficult" (B) does not relate to the symptoms being distinct. "Separate" (C) is a synonym for "discrete," making it a tempting distractor, but it is not the best fit in the context. "Common" (D) is the opposite of what is being described - the symptoms are distinct, not common. Therefore, the most appropriate choice is A: Individual.