Answer;
The A Horizon
Explanation;
-The major soil horizons are A, B, C and other soil types may have horizon O, which may be thick or thin and also not present in some soils.
-The A horizon is the uppermost layer in the soil profile. It is a weathered layer of the soil and is composed of an accumulation of humus and other microbial biomass which are mixed with minerals that are small-grained.