_________ energy is the main driving force of the ecological system.

Hydro energy, electric energy, and mechanical energy are all secondary forms of energy that are derived from solar energy. Hydro energy is the energy of moving water, which is caused by the sun’s heat. Electric energy is produced by the movement of electrons, which can be generated by solar cells or by other sources of energy, such as wind or water. Mechanical energy is the energy of motion, which can be produced by the sun’s heat or by other sources of energy, such as wind or water.

In conclusion, solar energy is the main driving force of the ecological system because it is the source of all other forms of energy on Earth.