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
A patient diagnosed to have deep vein thrombosis is being treated with heparin. Which of the following test will you order to adjust its dosage : 
Select and explain. 
A. Platelet count, B. Prothrombin time, C. Bleeding time, D. Activated partial thromboplastin time
D: Activated partial thromboplastin time
Answer: D: Activated partial thromboplastin time 
Explanation: None