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': 'Commonest site of lung abcess is- \nSelect and explain. \nA. Post segment of right upper lobe, B. Lingula, C. Post segment of left lower lobe, D. Post segment of right lower lobe', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]