In this model food web, grass captures sunlight, grasshoppers eat grass, frogs eat grasshoppers, and hawks eat frogs. What is the original source of the energy that eventually reaches the hawks?

الشرح

Only the grass in this web can take in energy from outside it; every animal above the grass gets its energy second-hand by eating. So the sunlight the grass captures is the single input that all the energy in the hawks traces back to. The closest wrong choice is mineral nutrients from decomposers: those recycle the matter the grass needs, but they carry no usable energy into the web.