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
One of the causes of finger clubbing is: 
Select and explain. 
A. Carcinoma of the lung, B. Cardiac failure, C. Bronchial asthma, D. Ischaemia heart disease
A: Carcinoma of the lung
Answer: A: Carcinoma of the lung 
Explanation: None