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
[{'content': 'Which of the following vitamin is required for the synthesis of blood clotting factors? \nSelect and explain. \nA. Vitamin K, B. Vitamin C, C. Riboflavin, D. Cobalamin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 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', 'role': 'assistant'}]