Concept:A soil profile shows soil layers from the surface down to the solid rock beneath.
Explanation:The layer labelled X is at the very bottom of the profile.
It lies below the parent materials.
This layer is made of solid, unweathered rock.
In a standard soil profile, the bottom layer is called the bedrock.
The topsoil is the dark surface layer, and the subsoil is the layer below it.
Parent materials are partly weathered rocks above bedrock.
Therefore, X is not topsoil, subsoil, or parent materials.
Answer:D. bedrock
