This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Transplantation, Subject name: Surgery
[{'content': 'Hyper acute rejection is due to: \nSelect and explain. \nA. Preformed antibodies, B. Cytotoxic T-lymphocyte medicated injury, C. Circulating macrophage mediate injury, D. Endothelitis caused by donor antibodies', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) Preformed antibodiesRef: Bailey 26th edition, Page 1412* Hyperacute happens in minutes to hours due to preformed antibodies.', 'role': 'assistant'}]