The materials cycled through ecosystems during the nitrogen cycle and the carbon cycle A. Remain at constant levels, although the form and location of the materials can change. B. Decrease steadily until more of the materials are added from outside systems. C. Increase or decrease based on the number of producers in the ecosystem. D. Remain at constant levels and cannot change form or location within the ecosystem.

The answer is A.

Explanation:

The carbon and nitrogen cycles can be broken down into the following steps. The nitrogen can be found in the soil, in the air, in plants and animals. It is transferred to a different body when a plant or an animal is eaten. Then the digestion happens and the nitrogen goes back to the soil, or water. Through this process the cycle is completed. Carbon cycle can follow the same path. These cycles also include the breathing of all organisms and the decomposition of all organisms and even rocks etc.

So the answer is A.

I hope this answer helps.

A. Remain at constant levels, although the form and location of the materials can change.

Explanation:

compost can be added to topsoil as a:

pesticide

when it is at an intermediate population density