The answer would be:
D. Reactant
In photosynthesis, light energy is considered as a reactant. The reactants of photosynthesis include, water, carbon dioxide and light energy. The sun provides the light energy needed, which is absorbed by the chloroplasts.
This is the chemical equation of photosynthesis:
12H20 + 6CO2 + light energy → C6H12O6 + 6H2O + 6O2
