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: Radiology
[{'content': 'Penetration power is more for \nSelect and explain. \nA. Hard X-rays, B. Soft X-rays, C. X-rays with long wavelength, D. Grenz rays', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]