A 27-year-old man with a recent history of drug abuse presented to the emergency department with violent , shaking chills. He also complained of rest lessness, insomnia, nausea, and abdominal cramps and exhibited profuse sweating, rhinorrhea, yawning, and piloerection. He admit ted he was out of money and was unable to get the usual supply of the drug he had been using for 3 months. From which of the following drugs was he most likely experiencing withdrawal? A. B. C.