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
'Bioavailability' is defined as: 
Select and explain. 
A. The volume of plasma completely cleared of a specific compound per unit time and measured as a test of kidney function, B. The percentage of drug that is detected in the systemic circulation after its administration, C. Both, D. None
B: The percentage of drug that is detected in the systemic circulation after its administration
Answer: B: The percentage of drug that is detected in the systemic circulation after its administration 
Explanation: None