You are answering a USMLE-style medical question. Question: A 34-year-old man currently staying at an addiction center presents to the staff psychiatrist with diarrhea and painful muscle cramps. He has been discontinuing heroin over the last month as part of his treatment plan. He is HIV positive, hepatitis B (HBV) positive, and was recently treated for an infection with Streptococcus pneumoniae. He reports pain over his abdomen, knees, and shoulder. To comprehensively treat these symptoms, which of the following would be the best therapy? Options: A) Methadone B) Naloxone C) Alvimopan D) Loperamide Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.