The correct option is D Chlorophyll concentration
The process of photosynthesis is influenced by several factors, which include both internal (plant) and external (environmental) factors. The plant factors include the number, size, age, and orientation of leaves, presence or absence of hormones, leaf anatomy, amount of chlorophyll, etc. The external factors would include the availability of sunlight, temperature, the concentration of CO2 and O2 and water. So, the correct answer is 'Chlorophyll concentration'.