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
Amount of drug left after four plasma half lives- 
Select and explain. 
A. 6.25%, B. 12.50%, C. 25%, D. 50%
A: 6.25%
Answer: A: 6.25% 
Explanation: Ans. is 'a' i.e., 6.25% Half life Drug left After 1 t'" 50% After 2 t'" 25% After 3 til2 125% After 4 t"2 6.25% After 5 ty2 3.125%