**Core Concept**
Female sterilization involves surgical procedures to block the fallopian tubes, preventing fertilization. The technique chosen depends on the surgeon's preference, patient's anatomy, and the desired level of reversibility. The most common site of ligation in female sterilization is a critical aspect of the procedure.

**Why the Correct Answer is Right**
The most common site of ligation in female sterilization is the ampulla of the fallopian tube. This is because the ampulla is the widest portion of the tube, making it easier to access and ligate. The ampulla is also the site where fertilization most commonly occurs, making it an ideal location for sterilization. The procedure, known as tubal ligation, involves blocking the ampulla using clips, rings, or sutures to prevent egg fertilization.

**Why Each Wrong Option is Incorrect**
* **Option A:** The isthmus is a narrower portion of the fallopian tube, making it more challenging to ligate. While it can be a site for sterilization, it is not the most common location.
* **Option B:** The interstitial portion of the fallopian tube is the portion that passes through the uterine wall. Ligation at this site is more complex and associated with higher risks of complications.
* **Option D:** The infundibulum is the funnel-shaped portion of the fallopian tube that contains the fimbriae. While it can be a site for sterilization, it is not the most common location due to its narrower diameter and more complex anatomy.

**Clinical Pearl / High-Yield Fact**
The key to successful female sterilization is proper identification and ligation of the ampulla of the fallopian tube. Surgeons should carefully inspect the fallopian tubes and choose the most accessible and safest site for ligation.

**Correct Answer:** C.