This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc., Subject name: Medicine
Medical treatment of gallstone indicated in A/E: 
Select and explain. 
A. GB should be functioning, B. Gallstone should be radiolucent, C. Gallstone should be radio opaque, D. Patient is unfit for surgery
C: Gallstone should be radio opaque
Answer: C: Gallstone should be radio opaque 
Explanation: For good results, medical therapy should be limited to radiolucent stones smaller than 5 mm in diameter. Stones larger than 15 mm in size rarely dissolve. Pigment stones are not responsive to UDCA therapy to produce a lamellar liquid crystalline phase in bile that allows a dispersion of cholesterol from stones. Ursodeoxycholic acid decreases cholesterol saturation of bile. UDCA may also retard cholesterol crystal nucleation.