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
Porosity in porcelain can be prevented by: 
Select and explain. 
A. Thoroughness of condensation, B. Rapidity of firing, C. High firing temperature, D. All of the above
A: Thoroughness of condensation
Answer: A: Thoroughness of condensation 
Explanation: None