Task: Question Answering
Input (English): Question: Oxidative phosphorylation involves: 
 Options:  <1> The oxidation of H2O to form O2. <2> Oxidation of O2 to form H2O. <3> The reduction of H2O to give O2. <4> The reduction of O2 to give H2O. <5> None of the above.
Output (English): 4