You are answering a USMLE-style medical question. Question: A 51-year-old man is brought to the physician by his wife because of a 3-week history of abnormal behavior. His wife reports he has been preoccupied with gambling at the local casino. He becomes restless and irritable when his wife attempts to restrict his gambling. Four months ago, he was diagnosed with Parkinson disease and treatment was initiated. Which of the following best describes the mechanism of action of the drug that was most likely prescribed for this patient? Options: A) Peripheral inhibition of DOPA decarboxylase B) Direct activation of dopamine receptors C) Selective inhibition of monoamine oxidase B D) Inhibition of catechol-O-methyl transferase Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.