The right option is a. variations.
Variations are the differences between the individual organisms of the same species which is as a result of genetic differences or the influence of environmental factors on the expression of the genetic abilities. Variation may be expressed in behavior, physical appearance, learning, and metabolism. The two types of variations are somatic variation and germinal variation.
Answer is c. Natural gas.
Natural gas is a fossil fuel in liquid form that can be used as an energy source. It is found in subterranean reservoirs, often near oil deposits. It is non-renewable energy source. It takes very long time to renew. Natural gas is less pollutant as compared to coal and petroleum because when it's burned, it releases 25 % fewer greenhouse gases and pollutants. hydroelectric power, solar power and nuclear energy are renewable sources.
Energy used since long time ago is a energy production system where the energy is joined with the new resources and alll of that turns into electric energy!<span />
Rough endoplasmic reticulum contains ribosomes, while smooth endoplasmic reticulum does not contain ribosomes. The ribosomes are what give rough endoplasmic reticulum its characteristic "roughness."
