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
The sac contains only a portion of the circumference of the intestine 
Select and explain. 
A. Richter's hernia, B. Littre's hernia, C. Spigelian hernia, D. Lumber hernia
A: Richter's hernia
Answer: A: Richter's hernia 
Explanation: None