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
Complete drug elimination occurs after how many hours, if t½ is 4 hrs.: 
Select and explain. 
A. 12 hrs., B. 20 hrs., C. 25 hrs., D. 30 hrs.
B: 20 hrs.
Answer: B: 20 hrs. 
Explanation: None