Question

write the answer here - hint it is one of the three things required for photosynthesis.

Explanation:

The three things required for photosynthesis are sunlight (or light energy), carbon dioxide ($\ce{CO_2}$), and water ($\ce{H_2O}$). Any of these can be a valid answer. For example, sunlight is essential as it provides the energy needed for the photosynthetic process.

Answer:

Sunlight (or Carbon Dioxide, or Water)