This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: CHF, Angina Pectoris and Myocardial Infarction, Subject name: Pharmacology
[{'content': 'Which of the following statements best explains the action of nitroglycerine on coronary vessels: \nSelect and explain. \nA. It mitigates angina pectoris by increasing total coronary flow, B. It preferentially dilates conducting aeries without affecting resistance aerioles, C. It preferentially dilates autoregulatory aerioles without affecting the larger aeries, D. It mainly decreases the after load', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Nitrates cause redistribution of blood flow without affecting total coronary flow. Autoregulatory small vessels remain unaffected whereas large conducting vessels are dilated. Nitrates are predominantly venodilators, therefore decrease mainly preload.', 'role': 'assistant'}]