You are answering a USMLE-style medical question. Question: A 57-year-old homeless man is brought to the emergency department because of several episodes of hematemesis in the past 24 hours. His vital signs include a temperature of 37.1°C (98.8°F), pulse of 95/min, and blood pressure of 85/60 mm Hg. On physical examination, he appears confused and unable to give a complete history. He is noted to have jaundice, palpable firm liver, mild splenomegaly, and shifting dullness consistent with the presence of ascites. Liver function tests are as follows: Serum aspartate aminotransferase (AST) 97 U/L Serum alanine aminotransferase (ALT) 40 U/L Serum albumin 2.5 g/dL Total bilirubin 3 mg/dL Prothrombin time 20 seconds Which of the following is the most likely cause of this patient's illness? Options: A) Metabolic disorder B) Substance abuse C) Obesity D) Hepatic venous outflow obstruction Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.