Which would have the greatest effect on the rate of photosynthesis in a plant? a) oxygen level b) light intensity c) sugar concentration d) starch concentration

The correct answer is option B, Light intensity

Reason -

Light intensity plays a major role in the regulation of photosynthesis. In the absence of light a plant is unable to photosynthesize. As the plant receives light through the chlorophyll , essential chemical reactions takes place thereby releasing free electrons which keep on driving the further processes or reactions in a plant to produce food and oxygen and energy..  

The higher the light intensity, the higher is the rate of photo synthesis

i think that it is plants