Human activities such as burning fossil fuels and deforestation primarily impact the carbon cycle by:

The correct answer to the question "Human activities such as burning fossil fuels and deforestation primarily impact the carbon cycle by:" is Option C: Releasing stored carbon dioxide into the atmosphere.

The other options — A) Decreasing the rate of photosynthesis, B) Increasing the amount of carbon stored in oceans, D) Reducing the overall carbon footprint of ecosystems — are incorrect for this IB Exam Prep question. As explained above: Burning fossil fuels releases carbon that has been sequestered for millions of years, while deforestation reduces the capacity of forests to absorb CO2, both contributing to increased atmospheric CO2.