The ultimate source of energy for most life on Earth is c) the sun.
This is primarily because the sun emits light that is captured by plants through the process of photosynthesis. During photosynthesis, plants convert solar energy into chemical energy, which is stored in the form of glucose and other carbohydrates. This energy then becomes the foundation of the food chain, as herbivores feed on plants and carnivores feed on those herbivores. Without the sun’s energy, there would be no plants, and consequently, no life as we know it.
While other sources of energy, like geothermal heat from the Earth or the metabolic processes of living organisms, play important roles in supporting life, they do not serve as the primary source of energy. Oxygen is essential for many life forms but is a byproduct of photosynthesis and not a source of energy itself. Therefore, the sun remains the ultimate energy source for nearly all living organisms on our planet.