i think the answer is c, rivers.
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.
answer placeholder because the system is messed up
your answer would be a) no nation can be economically self-sufficient.
stay in school!