**Core Concept**
The inguinal canal is a narrow passageway in the lower abdominal wall through which the spermatic cord (in males) or the round ligament of the uterus (in females) passes. The nerve that accompanies these structures is a branch of the lumbar plexus, providing sensory innervation to the skin of the medial aspect of the thigh and the root of the penis (in males) or the mons pubis and labia majora (in females).

**Why the Correct Answer is Right**
The correct answer is the ilioinguinal nerve (L1, L2), which arises from the lumbar plexus and passes through the inguinal canal. It provides sensory innervation to the skin of the medial aspect of the thigh and the root of the penis (in males) or the mons pubis and labia majora (in females). The ilioinguinal nerve also has a motor branch that innervates the cremaster muscle.

**Why Each Wrong Option is Incorrect**
* **Option A:** The genitofemoral nerve is another branch of the lumbar plexus, but it does not pass through the inguinal canal and is not responsible for the sensory innervation of the skin in this area.
* **Option B:** The femoral nerve is a branch of the lumbar plexus that provides motor innervation to the muscles of the anterior thigh and sensory innervation to the skin of the anterior thigh, but it does not pass through the inguinal canal.
* **Option C:** The obturator nerve is a branch of the lumbar plexus that provides motor innervation to the adductor muscles of the thigh and sensory innervation to the skin of the medial thigh, but it does not pass through the inguinal canal.

**Clinical Pearl / High-Yield Fact**
The ilioinguinal nerve is often responsible for referred pain in the testes (in males) or ovaries (in females) due to inflammation or irritation of the nerve.

**Correct Answer: D. Ilioinguinal nerve**