**Core Concept**
Referred pain in external hemorrhoids involves the perception of pain from the anal region being referred to other areas due to the convergence of visceral and somatic afferent fibers in the spinal cord. This phenomenon is characteristic of the spinal cord's ability to process and integrate sensory information from various sources.

**Why the Correct Answer is Right**
The inferior rectal nerve is a branch of the pudendal nerve that provides somatic innervation to the external anal sphincter and the skin around the anus. In the case of external hemorrhoids, the pain is referred to the perianal region due to the activation of nociceptors in the affected area. The inferior rectal nerve is responsible for transmitting this pain signal to the spinal cord, where it is perceived as referred pain. This is in contrast to internal hemorrhoids, which are innervated by the inferior mesenteric plexus and do not typically cause referred pain.

**Why Each Wrong Option is Incorrect**
**Option A:** The common pudendal nerve is a mixed nerve that provides both somatic and visceral innervation to the pelvic region, but it is not directly responsible for the referred pain associated with external hemorrhoids.

**Option C:** The splanchnic nerves are visceral afferent nerves that transmit pain signals from the abdominal viscera to the spinal cord, but they are not involved in the referred pain associated with external hemorrhoids.

**Option D:** The sympathetic nerves are part of the autonomic nervous system and play a role in the regulation of smooth muscle tone and blood vessel constriction, but they are not directly involved in the transmission of pain signals associated with external hemorrhoids.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the distinction between external and internal hemorrhoids is not just based on their location, but also on their innervation and the type of pain they cause. External hemorrhoids are typically associated with pain and bleeding, while internal hemorrhoids are often asymptomatic or cause only minor discomfort.

**✓ Correct Answer: B. Inferior rectal nerve**