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: Radiology
Rigler's triad is seen in 
Select and explain. 
A. Pneumo peritoneum, B. Intestinal obstruction, C. Gallstone ileus, D. Ulcerative colitis.
C: Gallstone ileus
Answer: C: Gallstone ileus 
Explanation: Gallstone ileus - Rigler's triad

Ectopic gall stone
Pneumobilia
Small bowel obstruction.