Answer:
The correct answer is option C. sunlight.
Explanation:
The Sun is the main source of energy for organisms, as the light energy or solar energy, the ecosystems.
Producers are autotrophs such as plants, and algae use the energy from solar light to make organic matter from water and carbon dioxide through the process of photosynthesis.
Hence, this establishes the initiating of energy flow through almost all ecosystems and food web.
Thus, the correct answer is option C. sunlight.