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
Conventional glazed dental porcelain is approximately ____times as abrasive as gold to tooth enamel 
Select and explain. 
A. 10, B. 20, C. 30, D. 40
D: 40
Answer: D: 40 
Explanation: Conventional glazed dental porcelain is approximately 40 times as abrasive as gold to tooth enamel