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': 'Role of nitrates in congestive cardiac failure is due to? \nSelect and explain. \nA. Direct inotropic action, B. Decrease preload, C. Decrease afterload, D. Coronary vasodilatation', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Decrease preload", 'role': 'assistant'}]