This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous System, Subject name: Radiology
[{'content': 'Investigation of choice for lactating female with a painful lump? \nSelect and explain. \nA. USG, B. CT, C. MRI, D. Mammogram', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A. USGPainful lump in a lactating female is suggestive of breast abscess. Ultrasound is the investigation of choice for differentiating cystic vs solid swelling.', 'role': 'assistant'}]