Final answer:
The combustion of fossil fuels significantly increases the rate of greenhouse gas emissions, unlike reforestation and sustainable agriculture practices which help reduce emissions.
Step-by-step explanation:
The process that can increase the rate of greenhouse gas emissions is C. Combustion of fossil fuels. This includes the burning of carbon-based energy sources like gasoline, coal, and natural gas. Such activities release carbon dioxide and methane into the atmosphere, which are potent greenhouse gases. Conversely, approaches like reforestation, carbon sequestration in soil, and sustainable agriculture practices are methods that reduce greenhouse gas emissions. Reforestation increases the number of trees that absorb carbon dioxide, while carbon sequestration in soil and sustainable agriculture aim to reduce emissions from agricultural practices.