What is the transportation barrier that divides the eastern part of russia

around the northern part of the globe, covering nearly half of two continents. It is a land of vast distances, bitter winters, and remote frontiers. The ancient Ural Mountains separate European Russia in the west from Asian Russia, or Siberia, in the east.

the europeans in the caribbean colonies had to turn to africans to replace the native peoples as slave it would be letter a

d is the logical answer but im not a 100% sure