**Core Concept**
The most common type of anorectal fistula is related to the **anatomy of the anal glands** and the **pathophysiology of anal abscesses**. Anorectal fistulas are abnormal connections between the inside of the anus and the skin around it.

**Why the Correct Answer is Right**
The most common anorectal fistula is the **intersphincteric fistula**, which occurs when an **abscess** forms in the **intersphincteric plane** and then drains to the skin, creating a fistula. This type of fistula is most common due to the anatomy of the anal glands and the direction of least resistance for the abscess to drain.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not specified, but other types like transsphincteric or suprasphincteric fistulas are less common.
**Option B:** Incorrect as it is not the most common type.
**Option D:** Incorrect because it is not the most frequent type of anorectal fistula.

**Clinical Pearl / High-Yield Fact**
Remember that **intersphincteric fistulas** are the most common and usually have a **straight, simple tract**. They are less complex compared to other types and often have a better prognosis with appropriate treatment.

**Correct Answer:** D. Intersphincteric fistula.