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: Gynaecology & Obstetrics
[{'content': 'Most useful investigation for VVF is: \nSelect and explain. \nA. Three swab test, B. Cystoscopy, C. Urine culture, D. IVP', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The most useful investigation in case of VVF is cystoscopy as it helps to confirm the size, position and number of fistulas.', 'role': 'assistant'}]