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
All the following will appear caries in an X-ray except 
Select and explain. 
A. Acrylic resin, B. Calcium hydroxide, C. ZOE, D. Composite
C: ZOE
Answer: C: ZOE 
Explanation: None