**Core Concept**
The inferior mesenteric artery (IMA) is responsible for supplying blood to the distal portion of the colon, including the sigmoid colon and rectum. During surgical procedures involving these regions, ligation of the IMA may be necessary to control bleeding or facilitate tumor removal.

**Why the Correct Answer is Right**
The correct answer is the inferior mesenteric artery because it is the primary blood supply to the descending colon, where the mass is located. The IMA originates from the aorta below the renal arteries and supplies the distal colon through its terminal branches, including the sigmoid and rectal arteries. Ligation of the IMA would effectively control bleeding from the mass in the descending colon.

**Why Each Wrong Option is Incorrect**
**Option A:** The superior mesenteric artery (SMA) supplies the proximal two-thirds of the transverse colon, the entire ascending colon, and the proximal third of the transverse colon. It is not responsible for supplying the descending colon.
**Option C:** The external iliac artery is a major artery that supplies the lower extremities and external genitalia, but it does not supply the colon.
**Option D:** The internal iliac artery supplies the pelvic organs, perineum, and external genitalia, but it does not supply the colon.

**Clinical Pearl / High-Yield Fact**
When performing surgical procedures involving the colon, it is essential to identify and ligate the correct arterial supply to control bleeding and prevent complications. The IMA is a critical artery to identify during surgeries involving the distal colon, and failure to ligate it can lead to severe bleeding.

✓ Correct Answer: B. Inferior mesenteric artery