Which term is used to collectively describe the O, A, E, and B soil horizons, excluding the R and C layers?

Explanation

The soil horizons O, A, E, and B together form the solum, which represents the true soil profile where soil formation processes actively occur. The R horizon refers to bedrock, and the C horizon is the parent material, both excluded from the solum. The outer and inner cores are parts of Earth's internal structure, unrelated to soil horizons.