**Core Concept**
The urogenital diaphragm is a layer of tissue in the pelvic floor that supports the urogenital organs. It is composed of the superficial and deep transverse perineal muscles, the perineal body, and the inferior fascia of the urogenital diaphragm. This structure plays a crucial role in maintaining the integrity of the pelvic floor.

**Why the Correct Answer is Right**
The urogenital diaphragm is pierced by the urethra, the deep transverse perineal artery, and the perineal branch of the pudendal nerve. The urethra passes through the urogenital diaphragm to reach the external urethral orifice. The deep transverse perineal artery and the perineal branch of the pudendal nerve also traverse this structure to supply the surrounding tissues.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the external iliac artery does not pierce the urogenital diaphragm. Instead, it enters the pelvic cavity through the obturator foramen and descends to supply the lower limb.

**Option B:** Incorrect because the obturator nerve does not pierce the urogenital diaphragm. It enters the pelvic cavity through the obturator foramen and descends to supply the adductor muscles of the thigh.

**Option C:** Incorrect because the internal iliac artery does not pierce the urogenital diaphragm. It enters the pelvic cavity through the greater sciatic foramen and supplies various structures in the pelvic cavity.

**Option D:** Incorrect because the internal pudendal artery pierces the urogenital diaphragm. It enters the pelvic cavity through the greater sciatic foramen and descends to supply the external genitalia.

**Clinical Pearl / High-Yield Fact**
The urogenital diaphragm is an important structure in the pelvic floor, and its integrity is crucial for maintaining continence and supporting the urogenital organs. Damage to this structure can lead to various complications, including incontinence and pelvic organ prolapse.

**Correct Answer:** D. The internal pudendal artery does pierce the urogenital diaphragm.