Select the BEST definition of "comorbidity"?

A. Any physiologic, diagnostic, or medical reasons that indicate that a specific medication, therapy, treatment, or plan of care would be undesirable, unwise, or impossible to prescribe for a patient's health
B. A pathological development that is not an inherent part of the presenting problem but that occurs in a patient during the management of a patient's presenting problem
C. The worsening in severity of a disease, syndrome, or any symptoms
D. Any disease, illness, or ill health that is separate from the presenting problem but that occurs at the same time as the presenting problem

D