Which does not correctly describe an achievement of the maya?
a. understood the concept of zero
b. had cities with populations in the thousands
c. kept records on knotted strings, or khipu
d. accurately predicted eclipses

The Mayan civilization did not keep records of their existence on knotted strings or khipu. The Mayan civilization had ample evidences of a written language found in their calendars and predictions. Khipu or quipu (Hispanic spelling) is a tradition practiced by the Incans. The purpose of which is to encode cryptic information through knotted strings hanging from horizontal cords.

The Incan civilization left historians with the monumental architectures, advanced technologies, and different social structures. However, historians are still bothered with the role the Khipu plays in Incan society as it is said to be hardly written documents that truly symbolize an advanced civilization with a concrete language like the Mayans.  

C4 i’m pretty sure