Task: Question Answering
Input (English): Question: Of the following statements of the electron transport chain. Which is true ?: 
 Options:  <1> An FADH molecule can generate up to 2.5 molecules of ATP. <2> One molecule of NADH can generate up to 1.5 molecules of ATP. <3> Electrons flow from more positive reduction potentials to more negative reduction potentials. <4> Complex II (used by FADH2) does not transfer protons to the intermembrane space. <5> Complex III uses copper (Cu) atoms as cofactors.
Output (English): 4