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
Features of intestinal obstruction : clinically/investigation by :a) Abdominal distensionb) Vomitingc) Fluid level in X-ray > 4d) Localized tendernesse) Diarrhea 
Select and explain. 
A. ac, B. a, C. ad, D. ab
D: ab
Answer: D: ab 
Explanation: About option 'c'
> 5 air-fluid levels in x-ray abdomen suggest intestinal obstruction
Grainger's Diagnostic radiology writes - "3 to 5 fluid levels less than 2.5 cm in length may be seen, particularly in the right lower quadrant, without any evidence of intestinal obstruction or paralytic ileus."