During the light-dependent reactions of photosynthesis, which process is directly responsible for the generation of a proton gradient across the thylakoid membrane?

• A. The absorption of light by chlorophyll in Photosystem I
• B. The cyclic flow of electrons within Photosystem II
• C. The movement of electrons through the cytochrome b₆f complex
• D. The conversion of NADP⁺ to NADPH