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: Dental
Incomplete casting is due to 
Select and explain. 
A. Narrow Sprue, B. Wide Sprue, C. Porous Material, D. Rapid Solidification Shrinkage
D: Rapid Solidification Shrinkage
Answer: D: Rapid Solidification Shrinkage 
Explanation: None