Final answer:
The total amount of carbon on Earth always stays the same according to the Law of Conservation of Matter.
Step-by-step explanation:
The Law of Conservation of Matter states that in any given system that is closed to the transfer of matter, the amount of matter in the system stays constant. This means that the total amount of carbon on Earth always stays the same.
While the burning of fossil fuels releases carbon back into the atmosphere, it does not increase the total amount of carbon on Earth. The carbon that is released during combustion originally came from the Earth and was part of the carbon cycle. Additionally, deforestation does reduce the number of trees that use carbon dioxide and store carbon, but this does not change the total amount of carbon on Earth either.
Therefore, the correct answer is C. The total amount of carbon on Earth always stays the same.