Why is using fossil fuels considered unsustainable?

Fossil fuels take millions of years to replenish

Fossil Fuel is limited it is like coal there is a limit and it won't last forever. This also contributes that it is not safe for the environment as well as the safety and health of people. This is similar to when there are many factories around an area there is going to be a high percentage of respiratory diseases such as asthma.

c. newton's third law of motion

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.