Final answer:
The Aztecs were not one of the nomadic cultures from the Inner Asian Steppe; they were a Mesoamerican culture, unlike the Xiongnu, Scythians, and Huns who were nomadic groups associated with the steppes.
Step-by-step explanation:
The student asked which culture was not one of the nomadic cultures that lived on the Inner Asian Steppe in the ancient world. The options were a) Xiongnu, b) Scythians, c) Huns, and d) Aztecs. Among these, the option that was not a part of the nomadic cultures from the Inner Asian Steppe is d) Aztecs. The Aztecs were a Mesoamerican culture that flourished in central Mexico in the post-classic period from 1300 to 1521. The other options, namely the Xiongnu, Scythians, and Huns, were indeed nomadic groups that were associated with the steppes. The Xiongnu and the Huns, in particular, are well-known for their interactions with settled societies in China and the Roman Empire, respectively.