Decomposition is the process by which break(s) down over time.
a. soil, sand, and rocks
b. dead plants and animals
c. mountains
d. natural gas

The correct answer is - b. dead plants and animals.

The decomposition is a process that appears only in the organic matter, thus the animals and the plants. Once the animals and the plants die, they start to decompose. The decomposition is triggered by the bacteria, which manages to decompose almost of the organic matter, apart from the bones.

Through this process, the dead animals and plants contribute to the natural fertilization of the soil, because that is the material from which the uppermost, fertile, humus layer of the soils is formed.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.

b a mature ovary of a plant.