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
A 50 year old male patient complains of tremors in his hand while working. Patient is a dentist and is working since 25 years. Lab investigations reveal urine mercury level at 200  microgm/L. Which of the following symptoms would been seen in this patient? 
Select and explain. 
A. Irritability, B. Kidney inflammation, C. Swollen gums, D. Nervous system disturbance
A: Irritability
Answer: A: Irritability 
Explanation: None