The graph shows how the rates of photosynthesis vary with light intensity for two groups of plants: plants that thrive in direct sunlight, and plants that thrive in the shade. the plants in both groups receive the same amount of water and are kept at the same temperature.

the rates of photosynthesis are plotted for sun plants and shade plants against light intensity. for both plants, the lines increase at first but then level off. the maximum value is greater for the sun plants than the shade plants.

for both groups of plants, what best describes the relationship between light intensity and rate of photosynthesis?

a. the rate of photosynthesis increases with light intensity, and might be limited by other factors such as water and temperature.
b. the rate of photosynthesis increases with light intensity, and it increases without limit.
c. the rate of photosynthesis is independent of light intensity, but may be limited by other factors such as water and temperature.
d. the rate of photosynthesis is at a maximum over a narrow range of light intensities.