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 threshold value for workers in the mercury industry is: 
Select and explain. 
A. 200 to 400 µg per day, B. 100 to 200 µg per day, C. 350 to 500 µg per day, D. 500 to 700 µg per day
C: 350 to 500 µg per day
Answer: C: 350 to 500 µg per day 
Explanation: The threshold value for workers in the mercury industry is 350 to 500 µg per day. 
Reference: Phillip’s Science of Dental Materials, Pg-361