Dan Is Visiting His Folks for Christmas and Having a Grand

Dan is visiting his folks for Christmas and having a grand time. Suddenly, in the middle of singing a Christmas carol, Dan's dad seems to change abruptly. His speech starts slurring, and he loses control of the right side of his body. He appears very confused, although this comes and goes, and at times, he is completely alert and aware. After some testing at the emergency room, Dan and his mom are likely going to be informed that his dad has had

A) a stroke.
B) Alzheimer's disease.
C) Pick's disease.
D) Korsakoff's syndrome.