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: Unknown
Which drugs needs continuous monitoring of prothrombin time? 
Select and explain. 
A. Aspirin, B. Lepirudin, C. Digoxin, D. Warfarin
D: Warfarin
Answer: D: Warfarin 
Explanation: Ref. KDT. Page. 624