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: Unknown
Hyperacute rejection occurs within: 
Select and explain. 
A. 12 hours, B. 2 weeks, C. 1 month, D. 3 months
A: 12 hours
Answer: A: 12 hours 
Explanation: Ref. Robbins Pathology. 9th edition. Page. 233
 
Hyperacute Rejection

This form of rejection occurs within minutes or hours after transplantation.
A hyperacutely rejecting kidney rapidly becomes cyanotic, mottled, and flaccid, and may excrete a mere few drops of bloody urine.
Immunoglobulin and complement are deposited in the vessel wall, causing endothelial injury and fibrin-platelet thrombi
Glomeruli undergo thrombotic occlusion of the capillaries, and fibrinoid necrosis occurs in arterial walls.
The kidney cortex then under- goes outright necrosis (infarction), and such nonfunctioning kidneys have to be removed.