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: Physiology
Citrate is a useful anticoagulant because of its ability to 
Select and explain. 
A. Buffer basic groups of coagulation factors, B. Bind factor XII, C. Bind vitamin K, D. Chelate calcium
D: Chelate calcium
Answer: D: Chelate calcium 
Explanation: None