flow of protons across an electrochemical gradient flow of tRNA across an electrochemical gradient exposure of ADP to electromagnetic waves exposure of carbohydrates to electromagnetic waves
I gave my students this multiple choice question: Which process drives most of the ATP synthesis in a chloroplast?

Only one answer is correct among these 4 choices:
- flow of protons across an electrochemical gradient
- flow of tRNA across an electrochemical gradient
- exposure of ADP to electromagnetic waves
- exposure of carbohydrates to electromagnetic waves

Could you tell me which one is correct?

flow of protons across an electrochemical gradient