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
Ischemia/reperfusion (I/R) injury is considered to be a MAJOR mechanism for organ transplant failure. Allopurinol is used in organ preservation as: 
Select and explain. 
A. Antioxidant, B. Preservative, C. Free radical scavenger, D. Precursor for energy metabolism
C: Free radical scavenger
Answer: C: Free radical scavenger 
Explanation: The most commonly used solution for organ storage and flushing is the University of Wisconsin solution that contains lactobionate, raffinose, adenosine (a precursor for ATP generation), magnesium sulfate (to retard calcium influx), glutathione (as an antioxidant), and allopurinol (to inhibit xanthine oxidase induced reactive oxygen species (ROS) formation). Ref: Immunobiology of Organ Transplantation edited by David S. Wilkes, William J. Burlingham, 2004, Page 548, 560.