**Core Concept**
The ureters traverse the pelvis, crossing the external iliac arteries and veins, and then enter the deep pouch of the broad ligament. They then pass through the ureteric tunnel in the bladder wall, where they are most vulnerable to injury during pelvic surgery. A uretero-vaginal fistula occurs when there is an abnormal connection between the ureter and the vagina, typically resulting from surgical trauma.

**Why the Correct Answer is Right**
The correct site of uretero-vaginal fistula is below the uterine artery in the Mackenrodt's ligament, also known as the cardinal ligament. This is due to the anatomical relationship between the ureters and the uterine arteries. As the ureters traverse the pelvis, they are closely associated with the uterine arteries, which run through the cardinal ligament. During pelvic surgery, such as hysterectomy, the ureters may be inadvertently injured at this site, leading to the formation of a uretero-vaginal fistula.

**Why Each Wrong Option is Incorrect**
**Option A:** Below infudibulopelvic ligament - While the infundibulopelvic ligament is an important landmark in pelvic anatomy, it is not the most common site for uretero-vaginal fistula formation.

**Option C:** Vaginal angle - The vaginal angle is not a specific anatomical landmark that is associated with uretero-vaginal fistula formation.

**Option D:** Above uterine aery - Uretero-vaginal fistulas are more likely to occur below the uterine artery, rather than above it.

**Clinical Pearl / High-Yield Fact**
When performing pelvic surgery, it is essential to identify and preserve the ureters, particularly in the region of the cardinal ligament, to avoid the risk of uretero-vaginal fistula formation.

✓ Correct Answer: B. Below uterine aery in the mackenrodts ligament