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 lower blood mercury level at which the earliest non specific symptom starts appearing at: 
Select and explain. 
A. 25 ng/ml, B. 35 ng/ml, C. 40 ng/ml, D. 45 ng/ml
B: 35 ng/ml
Answer: B: 35 ng/ml 
Explanation: None