This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: vitamins, Subject name: Biochemistry
Which of the following vitamin is required for the synthesis of blood clotting factors? 
Select and explain. 
A. Vitamin K, B. Vitamin C, C. Riboflavin, D. Cobalamin
A: Vitamin K
Answer: A: Vitamin K 
Explanation: VITAMIN K IS REQUIRED FOR SYNTHESIS OF BLOOD-CLOTTING PROTEINS Antagonists of vitamin K are used to reduce blood coagulation in patients at risk of thrombosis; the most widely used is warfarin. Reference: Harper; 30th edition; Page no: 553