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: Surgery
During embryonic development, prolapsed gut returns to the abdominal cavity by: 
Select and explain. 
A. 12th week, B. 15th week, C. 18th week, D. 20th week
A: 12th week
Answer: A: 12th week 
Explanation: During the sixth week of fetal development, the midgut grows too rapidly to be accommodated in the abdominal cavity and therefore prolapses into the umbilical cord. Between the tenth and twelfth weeks, the midgut returns to the abdominal cavity, undergoing a 270-degree counterclockwise rotation around the superior mesenteric aery. Because the duodenum also rotates caudal to the aery, it acquires a C loop that traces this path. Ref: Schwaz's principle of surgery 9th edition, chapter 39.