A student creates a model of a garden ecosystem by filling a plastic crate with garden soil. The student sows the seeds of three different plants into the soil, places the crate outside, and waters the plants regularly. A teacher tells the student that the model can be improved. What should the student do to improve the model?
A. Sow more seeds of the same plant in the crate.
B. Introduce several worms into the soil.
C. Change the location of the crate to a room without windows.
D. Decrease the amount of water given to the plants in the crate.