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: Pharmacology
A drug given at the loading dose of 20mg reaches plasma concentration of  0.5mg/L, If apparent volume of distribution is 40L, Calculate Bio availability of the drug 
Select and explain. 
A. 70%, B. 80%, C. 90%, D. 100%
D: 100%
Answer: D: 100% 
Explanation: None