Historians label an event as a turning point when it?

Marks a major social, economic, or political shift.

Explanation:

A turning point describes a moment in history where a major change happens. This change is usually decisive in nature, and forever alters the events that come after it. The concept of turning point is usually applied to positive social, economic or political changes. For example, the invention of the printing press can be seen as a turning point in the cultural history of Europe, as it positively changed society in a massive way.

i think the answer is c, rivers.

explanation:

sometimes, borders fall along natural boundaries like rivers or mountain ranges. for example, the boundary between france and spain follows the crest of the pyrenees mountains. for part of its length, the boundary between the united states and mexico follows a river called the rio grande. the borders of four countries divide africa’s lake chad: niger, chad, cameroon, and nigeria.

true

coz they had the rank system in society according to the economic power of the people