When day light hours are increased, the rate of photosynthesis

Answer: Option C

When daylight hours are increased, the rate of photosynthesis remains unchanged.
"When a process is conditioned as to its rapidity by several separate factors the rate of the process is limited by the pace of the slowest factor." Limiting factors are not limited to the condition of the species.
When during the day, light hours are increased, it does not affect the rate of photosynthesis much, therefore, the rate of photosynthesis remains unchanged.