This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'Nitroglycerine exerts beneficial effects in variant angina primarily by: \nSelect and explain. \nA. Coronary vasodilation, B. Decreased ventricular contractility, C. Reduction of cardiac preload, D. Reduction of cardiac afterload', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]