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: Microbiology
[{'content': 'Diagnosis of typhoid in the first week is by - \nSelect and explain. \nA. Widal test, B. Stool culture, C. Urine culture, D. Blood culture', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]