Based on the options provided, the most appropriate question that Charlie can answer using the diagram of a process that occurs within a cell is:
a) What are the inputs and outputs in the process of photosynthesis?
This question pertains to the diagram depicting photosynthesis, which typically illustrates the inputs (like sunlight, water, and carbon dioxide) and outputs (glucose and oxygen) of the process. The other options relate to cellular respiration or specific storage locations of molecules, which wouldn't be applicable if the diagram specifically represents photosynthesis.