In soil taxonomy, Great group is defined largely on the basis of

Answer: Option A

In soil taxonomy, the Great group is defined largely based on the Diagnostic surface horizon.
Soil taxonomy is a morphogenetic soil classification system using diagnostic horizons, soil moisture or temperature regimes, and features to infer pathways of soil genesis and formation. It employs a unique mnemonic system based on Greek, Latin or other root words for assigning names to taxonomic classes.