The best answer is (1)
Fossil fuels are commercially available as an energy source.
They are very easy to find. More and more extractions of fossil fuels is going on everyday. With advancement in science and technology, the refineries and extraction procedures have improved a lot. This makes their availability even better.
Fossil fuels are also easily combustible. Most combustion engines need to be powered with little amount of fuel to produce large amount of energy. Very large amounts of electricity can be generated from fossil fuels.
Answer: they have to maintain homeostasis, so they remove waste to do so..
As you stated before, cellulose is found throughout the cell walls of plant cells. Cellulose makes cell walls rigid, so that would indicate that cellulose is a carbohydrate.
