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
[{'content': 'Amount of drug left after four plasma half lives- \nSelect and explain. \nA. 6.25%, B. 12.50%, C. 25%, D. 50%', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 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%', 'role': 'assistant'}]