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
Which one of the following categories of dental materials has the highest thermal conductivity? 
Select and explain. 
A. Unfilled acrylic plastics, B. Gold alloys, C. Porcelains, D. Zinc phosphate cements
B: Gold alloys
Answer: B: Gold alloys 
Explanation: None