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 29 year old female patient complains of decayed tooth. Patient is 7 months pregnant and gives history of cavity preparation and restoration with amalgam done with 16,17,26,27,37. Intra-oral examination reveals proximal caries with 26. The upper limit of urinary mercury in this patient is?​ 
Select and explain. 
A. 1 microgm/L​, B. 2 microgm/L​, C. 3 microgm/L​, D. 4 microgm/L​
D: 4 microgm/L​
Answer: D: 4 microgm/L​ 
Explanation: None