You Are the Attending Physician in the ER

You are the attending physician in the ER. You are examining a 48-year-old man brought by his wife because of a recent change in his mental status. Physical examination shows horizontal and vertical nystagmus, bilateral facial nerve palsy, and truncal ataxia. The most likely explanation for these findings is a deficiency in which of the following vitamins?

A) folate
B) vitamin B₁
C) vitamin B₆
D) vitamin C
E) vitamin D