The correct option is D Sun
As
the demand for energy is increasing and conventional sources of energy such as
coal, petroleum, natural gas, etc. are depleting, non-conventional sources of
energy are more needed. Sun, wind, biomass, tidal energy, geo-thermal energy
and even energy from waste material are examples of non-conventional energy.
Sun is the biggest source of non-conventional energy. As sun is the source of
all energy on the earth, it produces plenty of solar energy. This energy is abundant,
renewable, pollution free and eco-friendly.