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: Surgery
Hyperacute graft rejection is caused by ? 
Select and explain. 
A. Preformed antibodies, B. T- lymphocytes, C. Macrophages, D. B - lymphocytes
A: Preformed antibodies
Answer: A: Preformed antibodies 
Explanation: Ans. is 'a' i.e., Preformed antibodies