Which best explains how mold is able to grow on an old piece of cheese in the refrigerator?

A. Mold is produced when the cheese ages and reacts with moisture in the air.

B. Mold is naturally contained within the cheese and spontaneously grows when the cheese becomes old.

C. Mold spores are present in the air, and the cheese provides the energy and building materials the mold needs to survive.

D. Mold spores are present in the air, and moisture in the air provides the energy and building materials the mold needs to survive.