**Core Concept**
The artery to the ductus deferens is a branch of the superior vesical artery, which is a part of the internal iliac artery's network. This artery supplies blood to the ductus deferens, a muscular tube that stores and transports sperm in males.

**Why the Correct Answer is Right**
The superior vesical artery arises from the internal iliac artery and provides blood supply to the bladder, prostate, and ductus deferens. It is a crucial branch for the perfusion of the pelvic organs. The artery to the ductus deferens is a smaller branch that specifically supplies the ductus deferens, allowing for its proper functioning. This is essential for male reproductive health.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the middle rectal artery is a branch of the internal iliac artery, but it primarily supplies the rectum and not the ductus deferens.

**Option B:** This option is incorrect because the inferior vesical artery is also a branch of the internal iliac artery, but it mainly supplies the lower part of the bladder and not the ductus deferens.

**Option D:** This option is incorrect because the external iliac artery is a major artery that supplies blood to the lower limb, but it does not have any branches that supply the ductus deferens.

**Clinical Pearl / High-Yield Fact**
The ductus deferens plays a crucial role in male fertility, and any damage to this structure can lead to infertility. The artery to the ductus deferens is essential for maintaining its proper function, making it a vital structure to consider in surgical procedures involving the pelvic region.

**Correct Answer: C. Internal iliac artery.**