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
Of the light produced by quartz — tungsten -halogen, only a small percentage is suitable for curing composite resin material and most is converted into heat. How much percentage of this light is useful for curing? 
Select and explain. 
A. 0.50%, B. 5%, C. 10%, D. 50%
A: 0.50%
Answer: A: 0.50% 
Explanation: None