You are answering a USMLE-style medical question. Question: A 32-year-old male presents to the ED with acute-onset chest pain. His blood pressure is 157/90 mmHg and his his pulse is 116/min. He appears anxious and agitated and a careful exam reveals dilated pupils and a perforated nasal septum. An EKG reveals ST segment elevation so he is urgently taken for cardiac intervention. Upon review, this patient reveals that he has not had care from a physician since he graduated from college. In the interim he has been largely unemployed and admits that he has recently been homeless. When asked directly, the patient admits to alcohol and marijuana use but denies illicit drug use. Which of the following best describes the mechanism of action of the agent most likely responsible for this patient's presentation? Options: A) Blocking reuptake of dopamine and norepinephrine B) Inhibiting breakdown of biogenic amines C) Antagonizing the NMDA receptor D) Inhibiting the GABA receptor Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.