You are answering a USMLE-style medical question. Question: A 40-year-old woman with Down syndrome comes to the physician for the evaluation of fatigue, progressive clumsiness when using her hands, and difficulty walking for 3 months. During this period, the patient has had several episodes of dizziness as well as double vision. She also reports that she has lost control of her bladder on several occasions lately. She has not had any trauma or weight changes. She lives with her sister and works as a cashier in a local retail store. She takes no medications. Her vital signs are within normal limits. On mental status examination, she is oriented to person and place only. There is moderate weakness of the upper and lower extremities. Sensory examination shows no abnormalities. Deep tendon reflexes are 3+ bilaterally. Babinski's sign is present bilaterally. Which of the following would most likely improve this patient's symptoms? Options: A) Administration of botulism antitoxin B) Surgical fusion of C1/C2 C) Administration of methylprednisolone D) Administration of pyridostigmine " Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.