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
Subsurface porosity is due to 
Select and explain. 
A. Thermal changes, B. Thickness of the resin, C. Lack of temperature, D. Packing past the dough stage
A: Thermal changes
Answer: A: Thermal changes 
Explanation: None