Amajor cause of the russian revolution of 1917 was a. defeat of germany in the russian campaign b. marriage of czar nicholas ii to a german princess c. existence of sharp economic differences between social classes d. appeal of marxism to the russian nobility

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.

not too sure on this one thinking tyo organize the division of africa