Final answer:
The Pipiltin (B) were not part of the commoners in the Aztec social hierarchy; they were the nobility, which was the highest social class.
Step-by-step explanation:
In the Aztec social hierarchy, the group that was not part of the commoners was the Pipiltin (B). The Aztec nobility, including the Pipiltin, occupied the top levels of society and were distinguished by their ancestry, wealth, and the roles they played in government and religious institutions. In contrast, the Macehualtin were commoners who primarily worked the land and provided services such as food for the military. Tlalmaitl were landed commoners, and slaves were at the very bottom of society, often having been sold into servitude due to debt or other economic hardships.