An action spectrum graph presented in the question shows the rate of photosynthesis at different wavelengths. An absorption spectrum shows the amount of light that different pigment molecules absorb at different wavelengths (Choice D).
In this action spectrum graph, the highest rates of photosynthesis are when blue light at 430nm and red light at 660nm is present. However, the highest between both lights is the blue light and not the red light (Choice A). Even though there are indeed two chlorophyll pigments, chlorophyll a and chlorophyll b, the peaks in this graph do not represent the number of pigments (Choice C).
The low rates of photosynthesis between blue and red light represent other pigments that also absorb light.
