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': 'The feature of benign nature of solitary pulnonary nodule –  a) 6cm size  b) Acute onset   c) Small speckts of calcification  d) Popcorn calcification \nSelect and explain. \nA. ab, B. bd, C. cd, D. abd', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]