Chemical energy sources are often portable and
provide large amounts of energy. fossil fuels are
one kind of chemical energy source. most of the
energy we use in the united states is generated
by the combustion of fossil fuels. however, fossil
fuel combustion adds greenhouse gases to the
atmosphere, mostly co2. one measure of the
total amount of greenhouse gases that are
emitted into the atmosphere each year is called a
carbon footprint. read this article to compare the
carbon footprint of an average person in the
united states to an average person around the
world.

answer:

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phylogenetic tree is the tree of life or evolution tree. it shows the different branches of evolution. the sequence goes like tissues - coelom - backbone - endoskeleton - segmentation

scientists have discovered that hiv does not cause aids by the virus's direct effect on the host's immune cells, but rather through the cells' lethal influence on one another. researchers from the gladstone institutes have revealed that hiv does not cause aids by the virus's