In Bacterial Photosynthesis, What Is One Way in Which the Proton

In bacterial photosynthesis, what is one way in which the proton gradient is created?

A) reduction of a quinone that causes uptake of two protons from the cytoplasm
B) the reduction of NADPH
C) the transfer of protons from NADH across the membrane via a shuttle system
D) the conversion of H₂O to H⁺
E) None of the answers is correct.