Task: Question Answering
Input (English): Question: The chemosmotic theory: 
 Options:  <1> It was proposed by Singer and Nicholson. <2> Explains the mechanism of phosphorylation at the substrate level. <3> It requires that the membranes in which it forms are closed compartments. <4> It does not explain the synthesis of ATP in photosynthesis. <5> It has nothing to do with redox reactions.
Output (English): 3