Final answer:
The main source of energy for living things on Earth is solar energy. Plants capture this energy through photosynthesis, which supports nearly all life on our planet.
Step-by-step explanation:
The main source of energy for living things on Earth is solar energy (C). Solar energy drives a multitude of processes essential to life on our planet. Through the process of photosynthesis, plants, algae, and cyanobacteria capture solar energy to create glucose and oxygen, which are essential for the survival of living organisms. The sun's energy also supports the hydrologic cycle, powers wind, and contributes to the creation of fossil fuels over millions of years. While combustion of fossil fuels does provide a significant amount of energy for human activities, it is not the main source of energy for living things in the context of natural biological processes.