Concept:The main energy source driving terrestrial ecosystems is sunlight.
Explanation:Plants use sunlight to produce food through photosynthesis.
This process converts solar energy into chemical energy stored in plant tissues.
When herbivores eat plants, they gain this energy.
Then carnivores obtain energy by eating herbivores.
In this way, solar energy flows through the entire food chain.
Unlike geothermal, hydroelectric, or nuclear power, sunlight is freely available and directly fuels primary production.
Therefore, the ultimate and major power source for most terrestrial ecosystems is the Sun.
Answer:C. solar energy