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: Medicine
[{'content': 'One of the causes of finger clubbing is: \nSelect and explain. \nA. Carcinoma of the lung, B. Cardiac failure, C. Bronchial asthma, D. Ischaemia heart disease', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]