The American Indian republics are an example of an important in Oklahoma history. A. era B. decade C. century D. period

D. period

Explanation:

The geological time scale was categorized in a different time frames with the highest being super eons. Further super eons consist of eons, and the eons contain eras. Eras consist of smaller time epochs, ages, and periods. This classification helps one understand that era is a larger span of time than a period. The fact that it is hard to express in terms of a specific year while researching or categorizing historical events and for this purpose, we use these words according to a specific situation.