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: Social & Preventive Medicine
[{'content': 'Cluster testing is useful in detecting cases of: \nSelect and explain. \nA. STD, B. Cancer, C. Diabetes, D. Measles', 'role': 'user'}, {'content': 'Answer: A \nExplanation: STD', 'role': 'assistant'}]