**Core Concept**
High and low fistula-in-ano are classifications based on the location of the internal opening of the fistulous tract in relation to the pectinate line (also known as the dentate line) in the anal canal. The pectinate line is an anatomical landmark that separates the anal canal into the upper, columnar-celled portion (above the pectinate line) and the lower, stratified squamous-celled portion (below the pectinate line).

**Why the Correct Answer is Right**
A high fistula-in-ano is characterized by an internal opening located above the pectinate line, typically in the upper anal canal. This is in contrast to a low fistula-in-ano, which has an internal opening located below the pectinate line, in the lower anal canal. The location of the internal opening is crucial in determining the classification and management of fistula-in-ano, as high fistulas are generally more complex and require more extensive surgical intervention.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the classification of fistula-in-ano based on the location of the internal opening.
* **Option B:** This option is incorrect because it does not accurately describe the classification of fistula-in-ano based on the location of the internal opening.
* **Option D:** This option is incorrect because it does not accurately describe the classification of fistula-in-ano based on the location of the internal opening.

**Clinical Pearl / High-Yield Fact**
It is essential for surgeons to accurately classify fistula-in-ano based on the location of the internal opening to determine the optimal surgical approach and minimize complications.

**Correct Answer: C.**