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
Bird's beak appearance is seen in: 
Select and explain. 
A. Testicular torsion, B. Volvulus, C. Meconium ileus, D. Ileal atresia
B: Volvulus
Answer: B: Volvulus 
Explanation: Sigmoid volvulus often can be differentiated from cecal or transverse colon volvulus by the appearance of plain x-rays of the abdomen. Sigmoid volvulus produces a characteristic bent inner tube or coffee bean appearance, with the convexity of the loop lying in the right upper quadrant (opposite the site of obstruction). Gastrografin enema shows a narrowing at the site of the volvulus and a pathognomonic bird's beak. Ref: Schwaz's principle of surgery 9th edition, chapter 29.