Answer: Sunlight
Step-by-step explanation: The amount of sunlight that is required should be appropriate in order to carry photosynthesis. The plants trap sunlight by the help of green pigment found in the leaves.
The intensity of sunlight is important to maintain the significant rate of photosynthesis in the plants.
The amount of sunlight also decides the temperature of the surrounding medium in which the plant grows.
So, it is a very important factor when it comes to plants for the process of photosynthesis besides water and carbon dioxide.