a. co-occurrence of two disorders
Comorbidity refers to more than one illness or disease that is occurring in one person at the same time while on the other hand, multimorbidity is defined as more than two illnesses or diseases that is occurring in the same person at the same time means one person has three, four or more diseases at the same time. In this Comorbidity condition, a patient is suffering from two disease at the same time due to many factors.
So we can conclude that option A is the right answer.
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