Crop Plants Can Have Higher Densities of Stomata on the Underside

Crop plants can have higher densities of stomata on the underside of their leaves than on the surfaces of their leaves. Some scientists hypothesize that that the evolution of this adaptation enhanced the ability of these plants to regulate the rate of CO₂ uptake for each surface.
-You designed and performed an experiment that measured CO₂ gas exchange levels at the upper side of a sunflower leaf (fewer stomata) and the bottom side of a sunflower leaf (greater stomata) . After collecting and analyzing your data, you conclude that there was not a significant difference in CO₂ gas exchange between the two sides of the leaf. Which of the following possibly explains this finding?

A) The difference in the density of stomata on the two leaf surfaces is not likely due to an adaptation related to gas exchange regulation.
B) The difference in the density of stomata on the two leaf surfaces is likely due to specific mechanisms that sunflowers use to disperse their seeds.
C) The difference in the density of stomata on the two leaf surfaces is likely due to mycorrhizal associations with other plants.
D) The difference in the density of stomata on the two leaf surfaces is likely due to different pollination needs for each surface.