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: Unknown
[{'content': 'Which of the following is the most common complication of heart failure? \nSelect and explain. \nA. Hydrothorax, B. Pneumothorax, C. Pyothorax, D. Hemothorax', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The elevation of hydrostatic pressure in congestive heart failure causes transudation of fluid into the pleural cavity and, therefore, hydrothorax.', 'role': 'assistant'}]