Which of the following was used by both the aztec civilization and the spanish?
pyramid structures to honor religious figures
the nahuatl language for formal communication
a written calendar with religious observances
a numerical system organized by tens

Correct

A written calendar with religious observances

Spanish civilization made use of the calendar as did the Aztec civilization. However, the interruption of the notations some centuries before the conquest of Mexico by Spain means that all attempts to relate the Christian calendar to civilization are uncertain.

As an additional fact, through the use of Spanish, the 20-day period of the Aztec calendar is commonly known as twenty.

d.prevent the spread of communism outside of eastern europe.