You are answering a USMLE-style medical question. Question: A 70-year-old man is brought to the physician by his daughter because of increasing forgetfulness over the past 3 years. Initially, he used to forget his children's names or forget to lock the house door. During the past year, he has gotten lost twice while returning from the grocery store and was unable to tell passersby his address. One time, he went to the park with his granddaughter and returned home alone without realizing he had forgotten her. His daughter says that over the past year, he has withdrawn himself from social gatherings and avoids making conversation. He does not sleep well at night. His daughter has hired a helper to cook and clean his home. On mental status examination, he is oriented only to person. He describes his mood as fair. Short- and long-term memory deficits are present. He appears indifferent about his memory lapses and says this is normal for someone his age. The most appropriate initial pharmacotherapy for this patient is a drug that acts on which of the following neurotransmitters? Options: A) γ-aminobutyric acid B) Acetylcholine C) Dopamine D) Glutamate Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.