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
The carat of gold foil used for restoration: 
Select and explain. 
A. 24, B. 18, C. 20, D. 16
A: 24
Answer: A: 24 
Explanation: The direct filling gold is 99.99% pure which is similar to 24 carat gold. Carat refers to the parts of pure gold in 24 parts of an alloy. 24-karat gold is pure gold, whereas 22-karat gold is an alloy containing 22 parts pure gold and 2 parts of other metals.