Which would best explain why early communities in a region have little contact with other cultures?

People settle near a river where it empties into the sea.

The natural features in an area include high mountains, large deserts, and oceans.

A large river floods annually.

A river and its tributaries change course over time.

The natural features in an area include high mountains, large deserts, and oceans.

Explanation:

Certain groups of people in the process of evolution were cut off from civilization, due to the geographical barrier in the form of mountains or deserts, i. e., in hard to reach areas. The mountains thus served as a natural dam on the paths of ancient communities. Usually hill tribes lived in small dispersed villages, sometimes connected only by narrow mountain paths. In communities cut off from each other, their specific customs developed.