California Teacher Credentialing Examination (CSET) Practice Test 2025 - Free CSET Practice Questions and Study Guide

The significant achievement of the Olmec civilization is indeed the development of the first calendar in America. The Olmecs, considered one of the earliest Mesoamerican civilizations, are credited with creating one of the first sophisticated writing systems and contributing to the development of a calendar that tracked the cycles of the moon and the sun. This accomplishment was crucial for their agricultural practices, religious ceremonies, and societal organization as it helped them to plan activities and mark important cultural events.

In focusing on this achievement, it's essential to understand that the Olmecs laid the groundwork for later civilizations, including the Maya and Aztecs, who built upon their innovations in timekeeping and calendrical systems. The other answers relate to later civilizations or different geographic regions altogether, emphasizing that while the Olmecs had many notable contributions, their pioneering work with the calendar stands out in the context of their civilization's legacy.