Most Surgeons Never Expected Barnard to Transplant a Heart Because

Most surgeons never expected Barnard to transplant a heart because the problem of ____________ had not yet been solved.

A) post-transplant psychosis
B) formation of clots on any plastic surface or seam in contact with blood
C) how to control immune rejection of the transplanted organ without letting lethal organisms invade the patient's body
D) whether society would pay for heart transplants
E) fairness in selection of who would receive organs and who would not