<s>[INST] context: The ileum can become ischemic when arterial supply from the superior mesenteric artery is compromised. The superior mesenteric artery arises from the aorta posterior to the neck of the pancreas. It descends across the third part of the duodenum and enters the root of the mesentery behind the transverse colon. This artery gives origin to the following branches: inferior pancreaticoduodenal artery, middle colic artery, ileocolic artery, right colic artery, and intestinal arteries. The ileocolic artery descends behind the peritoneum toward the right and ends by dividing into the ascending colic artery, anterior and posterior cecal arteries, the appendicular artery, and ileal branches. The ileum is supplied by the ileal branches, which do not have any anastomoses with another major source vessel. The transverse colon is supplied by the marginal artery, which possesses anastomoses of the right colic artery arising from the superior mesenteric artery, and the left colic artery arising from the inferior mesenteric artery. The spleen, stomach, and duodenum are all supplied by branches of the celiac trunk, which arise from the abdominal aorta just below the aortic hiatus of the diaphragm. [/INST] question: A 62-year-old woman is admitted to the emergency department with abdominal pains of uncertain origin. A CT scan reveals an aortic aneurysm affecting the origin of the superior mesenteric artery, resulting in ischemia to an abdominal organ. Which of the following organs is most likely affected? | options: A: Ileum B: Transverse colon C: Spleen D: Stomach | answer: A </s>