Question

this is a loose mixture of rock fragments and organic material that can support the growth of vegetation . gravel compost soil sand

Explanation:

The description is about a loose mixture of rock fragments and organic material that supports vegetation growth. Soil is defined as such a mixture, while gravel, sand, and compost don't fully match this definition (gravel is coarser, sand lacks sufficient organic matter for broad vegetation support, compost is more decomposed organic matter without the rock fragment mix in the right way for this definition).

Answer:

soil