**Core Concept**
External hemorrhoids below the dentate line are characterized by their location in the anal canal, specifically below the pectinate line (dentate line). This area is lined with squamous epithelium, which is less sensitive to pain. External hemorrhoids in this region are typically painful due to the presence of nerve endings.

**Why the Correct Answer is Right**
Pain in external hemorrhoids below the dentate line is due to the innervation by the inferior rectal nerves, which are branches of the pudendal nerve. These nerves transmit pain signals to the spinal cord, causing discomfort and pain. The presence of pain is a key feature that distinguishes external hemorrhoids below the dentate line from those above it, which are typically painless due to the absence of nerve endings.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because external hemorrhoids above the dentate line are typically painless, not painful.
* **Option B:** This option is incorrect because internal hemorrhoids are located above the dentate line and are typically painless, not painful.
* **Option D:** This option is incorrect because thrombosed external hemorrhoids can be painful, but the question specifically asks about external hemorrhoids below the dentate line.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the location of hemorrhoids (above or below the dentate line) determines their likelihood of being painful. External hemorrhoids below the dentate line are typically painful, while those above it are usually painless.

**Correct Answer: C. Painful**