This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
Smallest cross-section of large bowel is seen at: 
Select and explain. 
A. Descending colon, B. Ascending colon, C. Transverse colon, D. Sigmoid colon
D: Sigmoid colon
Answer: D: Sigmoid colon 
Explanation: (Refer: Richard S. Snell’s Clinical Anatomy by Regions, 9th edition, pg no: 158)
Characteristic Features of Rectosigmoid Junction

The diameter of the large intestine narrows.
There is an absence of complete peritoneal investment.
There is no true mesentery.
The three taeniae coli diverge to form a continuous longitudinal muscle coat on the rectum.
There are no appendices epiploicae.
Endoscopically, an acute angle is encountered at the narrowing of the rectosigmoid and the rectal mucosa is smooth and flat, whereas the mucosa of the sigmoid forms prominent rugal folds.