Final answer:
The ileum is not a segment of the large intestine; it is part of the small intestine, making option D the correct answer.
Step-by-step explanation:
The question is asking which of the listed options is not a segment of the large intestine. The components of the large intestine include the cecum, colon (with its parts: ascending colon, transverse colon, descending colon, and sigmoid colon), and rectum. The ileum, however, is part of the small intestine, not the large intestine. Therefore, the correct answer is D. Ileum.