Task: Question Answering
Input (English): Question: COMPLETE: in the Krebs cycle 4 oxidation reactions occur, in 3 of them the final acceptor electron is ___ and in the other is ___: 
 Options:  <1> FAD / FMN. <2> NAD + / FMN. <3> NADP + / FAD. <4> NAD + / FAD. <5> FAD / NAD +.
Output (English): 4