Before the arrival of Europeans, the two most powerful and most populous empires in the Americas were those commonly referred to as the (based in the Andes Mountains) and the (based in central Mexico).

The empires that fills the blanks are:

Before the arrival of Europeans, the two most powerful and most populous empires in the Americas were those commonly referred to as the Incas (based in the Andes Mountains) and the Aztecs (based in central Mexico).

Explanation:

The Inca empire was one of the largest that encompassed part of Ecuador, Peru, Bolivia, Chile and Argentina (the vast majority of these countries have the Andes mountain range, which is why the Inca settlement was on that mountain range), on the other hand the Aztecs or Mexicas were settling in the central and southern of Mexico, precisely a curious fact of this pre-Hispanic town is that Mexico City is the place of one of its most significant legends of how they decided the place to reside.

sumerians were polytheistic, meaning they believed in many different gods. so, the best answer is c.