**Core Concept**
The perineum is a region of the body between the pubic symphysis and the coccyx, and its nerve supply is crucial for sensation and motor control in this area. The nerve supply to the perineum involves branches from the pudendal nerve, which arises from the sacral spinal cord.

**Why the Correct Answer is Right**
The correct answer is related to the innervation of the perineum by the pudendal nerve, which is a branch of the sacral plexus. The pudendal nerve originates from the S2-S4 nerve roots and provides motor innervation to the external anal sphincter, bulbospongiosus, and ischiocavernosus muscles, as well as sensory innervation to the perineal skin. The pudendal nerve also gives off branches to the skin of the perineum, including the scrotum and labia majora.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the hypogastric nerve is primarily involved in the sympathetic innervation of the pelvic organs, rather than the motor and sensory innervation of the perineum.
**Option B:** This option is incorrect because the obturator nerve is primarily involved in the innervation of the adductor muscles of the thigh, rather than the perineum.
**Option C:** This option is incorrect because the ilioinguinal nerve is primarily involved in the innervation of the skin of the groin and pubic symphysis, rather than the perineum.

**Clinical Pearl / High-Yield Fact**
The pudendal nerve is often tested during an anorectal examination, where the nerve is stretched and irritated, causing pain in the perineal region. This is a common examination maneuver used to assess the integrity of the pudendal nerve.

**Correct Answer: A. Pudendal nerve.**