How to tell is a molecule is oxidized or reduced?

It's true that NADH is becoming oxidized in the equation, but that does not mean it is the oxidant. The oxidant is the compound that DOES the oxidizing. In other words, it is the compound that took the electron. The same goes for the reductant, in the opposite respect. It is the compound the DOES the reducing. Neither A nor B are true. Therefore, the answer is E. In the equation, NADH is the reductant and FAD is the oxidant.