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
Before inserting the loaded tray with impression compound the temperature is usually checked: 
Select and explain. 
A. Against the back of operator’s hand, B. Against the hand of patient, C. By placing directly in mouth, D. By immersion in boiling water
A: Against the back of operator’s hand
Answer: A: Against the back of operator’s hand 
Explanation: None