You are answering a USMLE-style medical question. Question: A 24-year-old man is brought to the emergency department by the police. He was found unconscious and covered in bruises outside of a local bar. The patient has a past medical history of polysubstance abuse, depression, multiple suicide attempts, neuropathic pain, and schizophrenia. As part of the patient’s initial workup, a head CT is performed which is unremarkable, and an arterial blood gas is performed as seen below: pH: 7.29 PaCO2: 95 mm Hg PaO2: 70 mm Hg Bicarbonate: 24 mEq/L Which of the following is the most likely etiology of this patient’s current presentation? Options: A) Amitriptyline B) Cocaine C) Ethylene glycol D) Heroin Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.