What Is the General Effect of Humans on the Nitrogen

What is the general effect of humans on the nitrogen (N) and phosphorus (P) cycles?

A) We greatly increase levels of N and P through the burning of fossil fuels.
B) We cause levels of N and P in the environment to drop through our farming practices.
C) We use a great deal of N and P in our farming practices, causing high levels of both nutrients to enter the natural environment.
D) We deplete levels of N and P in our farming practices and do not replenish them.