I know you tried, I know you're cursed, I know your best was still your worst

The day before my sister's wedding I administered an exam in the night class I'm teaching. I didn't grade them until I got back. When I did get them graded, I saw something that depresses me greatly. It involves the following question (which I'd gone over three different times in class):

During aerobic respiration, which of the following molecules directly donates electrons to the electron transport chain at the lowest energy level, and thus only generates two ATP molecules?
A) NADH
B) FADH2


Two students chose D.

I wish I was joking.