Which of the following time spans is 20 years?

The correct answer is based on the definitions of the terms used in the context of the Mayan calendar system. A "Katun" specifically refers to a period of 20 years. In the classic Mayan civilization, the calendar was organized into various time units, and the Katun is one of those significant periods, alongside others like the Baktun and Tun which represent longer or shorter time spans, respectively.

The Baktun consists of 400 years, while the Tun represents a period of 360 days, which could also be associated with a yearly cycle but does not equate to 20 years. The term “Final” does not correspond to a standard time unit in this context and thus lacks relevance to the time spans under discussion. Understanding these units is crucial for grasping the structure of the Mayan calendar and how the culture perceived time.