Natural gas (methane (CH4)) is the cleanest burning fuel<span>, emitting the smallest amount of carbon dioxide of all the </span>fossil fuels<span> (coal, oil and natural gas).</span>
Its because a long spine cacti can reproduce more because it has more survival capacity than the short spine cacti and because of this reason the short spine cacti cannot protect it self because it has a shorter spine that could protect itself from danger.
Natural selection<span> is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations.</span>
