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: Medicine
The mechanism of action of Rivaroxaban, used in the treatment of heparin induced thrombocytopenia and thrombosis syndrome is: 
Select and explain. 
A. Direct factor Xa inhibitor, B. Activated factor VIIa, C. Vitamin K antagonist, D. None of the above
A: Direct factor Xa inhibitor
Answer: A: Direct factor Xa inhibitor 
Explanation: Rivaroxaban is the first orally active Factor Xa inhibitor. Useful in Heparin induced thrombocytopenia and thrombosis syndrome. Ref: Harrisons principles of internal medicine, 18th edition, Page 2737