You are answering a USMLE-style medical question. Question: A 67-year-old man is brought to the hospital by his relatives. He complains of early satiety, abdominal discomfort after food intake, and abdominal bloating. These symptoms have been present since the patient was 52, but they were milder at that time so he paid little attention to them since. Tingling and decreased sensation in both lower extremities began a few months ago. His relatives also note that he has become excessively somnolent and forgetful. The patient’s medical history is significant for acute hepatitis B 20 years ago. He smokes a pack of cigarettes per day and drinks alcohol occasionally. His weight is 61 kg (134.5 lb), height is 181 cm (5 ft 11 in), and BMI is 18.6 kg/m2. His vital signs include: blood pressure 110/80 mm Hg, heart rate 89/min, respiratory rate 13/min, and temperature 36.1°C (96.9°F). The patient’s skin is pale, thin, dry, and hypoelastic. Lymph nodes and the thyroid gland are not enlarged. Lung and heart examinations are within normal limits for his age. The patient’s tongue is bright red with atrophic papillae. The abdomen is distended and tender to palpation in the epigastric area. Neurological examination shows symmetrical bilateral distal hypoesthesia for all sensations and decreased muscle strength in both upper and lower extremities. On a mini-mental status examination, the patient scores 25. The patient’s blood test results are as follows: Erythrocytes 2.8 x 109/mm3 Hb 8.6 g/dL Ht 37% Mean corpuscular hemoglobin 49.9 pg/cell (3.1 fmol/cell) Mean corpuscular volume 142 µm3 (142 fL) Reticulocyte count 0.3% Total leukocyte count 3,070/mm3 Neutrophils 54% Lymphocyte 32% Eosinophil 3% Monocyte 11% Basophil 0% Platelet count 195,000/mm3 HbA1C 4.3% Fasting plasma glucose 4.6 mmol/l (82.9 mg/dL) Aspartate aminotransferase 22 U/L Alanine aminotransferase 19 U/L Amylase 32 U/L Total bilirubin 32 µmol/L (1.87 mg/dL) Conjugated bilirubin 8 µmol/L (0.4677 mg/L) Which of the following options best explains the patient’s neurological and psychiatric symptoms? Options: A) Chronic bilirubin toxicity B) Chronic acetaldehyde influence C) Impaired methylation of myelin phospholipids D) Influence of pseudo-neurotransmitters Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.