**Core Concept**
The anal canal is divided into three parts based on its lining, with the middle 1.5 cm being a critical area for understanding colorectal anatomy.

**Why the Correct Answer is Right**
The correct answer is related to the transition from the columnar epithelium of the rectum to the stratified squamous epithelium of the anal canal. The middle 1.5 cm of the anal canal is lined by columnar epithelium, which is continuous with the rectal mucosa. This area is often referred to as the pecten, a transitional zone where the anal glands and ducts open. The anal glands and ducts produce mucin, which helps to lubricate the anal canal and prevent irritation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the upper 1-2 cm of the anal canal is lined by columnar epithelium, not the middle 1.5 cm.

**Option B:** This option is incorrect as the distal 1 cm of the anal canal is lined by stratified squamous epithelium, not the middle 1.5 cm.

**Option D:** This option is incorrect as the anal verge is the distal 1 cm of the anal canal, which is lined by stratified squamous epithelium.

**Clinical Pearl / High-Yield Fact**
The middle 1.5 cm of the anal canal is a critical area for understanding colorectal anatomy, and its lining is continuous with the rectal mucosa. This area is often involved in conditions such as anal fistulas and abscesses.

**Correct Answer: C. Columnar epithelium.**