Final answer:
The correct answer is option C.Olmec.
Step-by-step explanation:
The group that most directly influenced both the Maya and the Aztec civilizations is the Olmec. The Olmec civilization, which preceded these cultures, is often referred to as the "mother culture" of Mesoamerica. They thrived in the region of Mexico from about 1200 B.C.E. to 400 B.C.E., and their influence is evident in aspects such as religious deities, the ritual ball game, calendar systems, and potentially their writing system.
While there is a debate about the extent of the Olmec's influence, it is clear that they set forth many cultural and religious practices that were adopted and adapted by subsequent civilizations like the Maya and Aztec. For example, the Maya calendar, which consisted of the 260-day Sacred Round calendar and the 365-day Vague Year calendar, was influenced by the Olmec. Similarly, the Aztecs also incorporated Olmec deities into their own pantheon, such as the feathered serpent, which the Aztecs called Quetzalcoatl.
In regards to the development of a writing system in the Western Hemisphere, the Olmec are believed to have created one of the first, which greatly contributed to the recording of history and genealogies in Mesoamerica.