**Core Concept**
Rotation of sigmoid volvulus occurs due to the mesenteric attachment of the sigmoid colon, which allows it to twist around its mesenteric axis. This twisting leads to obstruction of the sigmoid colon and subsequent ischemia. The sigmoid mesocolon, a broad, thin fold of peritoneum, attaches the sigmoid colon to the left side of the abdominal wall.

**Why the Correct Answer is Right**
The sigmoid colon's mesenteric attachment creates a long, narrow pedicle that is prone to twisting. This twisting event is facilitated by the sigmoid colon's position within the pelvis and its relatively long mesentery. As the sigmoid colon twists, the mesenteric vessels become compromised, leading to ischemia of the bowel wall. The twisting motion can be further exacerbated by the presence of a redundant sigmoid colon or a pre-existing inflammatory process.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the sigmoid colon's rotation is not primarily due to its attachment to the pelvic sidewall. While the pelvic sidewall does play a role in the sigmoid colon's position, it is not the primary factor in the development of sigmoid volvulus.

**Option B:** This option is incorrect because the small intestine's mesenteric attachment does not allow it to twist in the same way as the sigmoid colon. The small intestine's mesentery is shorter and more robust, making it less prone to twisting.

**Option C:** This option is incorrect because the transverse colon's mesenteric attachment is not as long and narrow as the sigmoid colon's mesentery. The transverse colon's mesentery is also more robust and less prone to twisting.

**Clinical Pearl / High-Yield Fact**
Sigmoid volvulus is a medical emergency that requires prompt recognition and treatment to avoid bowel necrosis. The "coffee bean" sign on abdominal X-ray is a classic radiographic finding in sigmoid volvulus, indicating the twisted sigmoid colon.

**Correct Answer: C**