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: Social & Preventive Medicine
Half life of lead in bone is: 
Select and explain. 
A. 1 year, B. 10 years, C. 20 years, D. None of the above
C: 20 years
Answer: C: 20 years 
Explanation: The half-life of lead compounds in the human body is, as a general rule, long, but it varies according to the tissue. Besides, it is almost impossible to determine its elimination rates, since the bones may have a large quantity ready to mobilize into the blood stream. Neveheless, some halflives are known for blood (3-4 weeks) and bones (20-27 years). Ref: