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
How to differentiate obstruction from paralytic lens? 
Select and explain. 
A. Absence of rectal gas shadow, B. Abdominal distension, C. Elevation of hemidiaphragm, D. Multiple air fluid levels
A: Absence of rectal gas shadow
Answer: A: Absence of rectal gas shadow 
Explanation: In x-ray of mechanical obstruction, there will be absence of rectal gas shadow.