Which of the Following Occurrences Would Be Classified as a Sentinel

Which of the following occurrences would be classified as a sentinel event?

A) A postpartum patient who elects to breastfeed only twice daily develops mastitis.
B) A newly diagnosed diabetic patient self-injects insulin in the abdominal area rather than the upper thigh as instructed by the patient educator.
C) A nurse assisting with the delivery of twins places the "Twin 1" name tag on the second-born twin, causing the first-born twin to undergo surgery that was scheduled for the other twin.
D) A nurse administers 3 units of regular insulin rather than 3 units of NPH insulin subcutaneously, resulting in a drop in the patient's serum glucose from 160 mg to 100 mg.