Your Elderly Grandfather Is Deteriorating

Your elderly grandfather is deteriorating. At first, he seemed only mildly forgetful, but lately he has had trouble recalling the names of close relatives and cannot remember where he is. He used to be very loving and patient, but now he is very unpleasant, and his condition is worsening. He is MOST likely experiencing:

A) presenile delirium.
B) intellectual developmental disorder.
C) Alzheimer's disease.
D) stroke-induced neurocognitive disorder.