This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urogynecology, Subject name: Gynaecology & Obstetrics
[{'content': 'Most useful investigation for VVF \nSelect and explain. \nA. Three swab test, B. Cystoscopy, C. Urine culture, D. IVP', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Big fistula Fistula tract is available Obvious escape of urine Tiny fistula Dye test Knee chest position: Escape of bubbles on coughing Three-swab test Gold Standard Cystoscopy Ref: D.C.DUTTA&;S TEXTBOOK OF GYNAECOLOGY; 6th edition; Pg no: 420', 'role': 'assistant'}]