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
Most useful investigation for VVF 
Select and explain. 
A. Three swab test, B. Cystoscopy, C. Urine culture, D. IVP
B: Cystoscopy
Answer: B: Cystoscopy 
Explanation: 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