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': 'Isotope selectively concentrated in abscess cavities: \nSelect and explain. \nA. Gallium, B. Technetium, C. Selenium, D. Chromium', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Gallium', 'role': 'assistant'}]