When hungary opened its borders, it created a "hole" in the

"Iron Curtain". Let me explain you. A quarter of a century ago, the Hungarian reformers began to break the fence on the border with Austria, making a hole in the "Iron Curtain". The Iron curtain was pulled off when Hungary opened the borders with Austria, and the Berlin Wall fell, reuniting Europe.

(d) rivers.

explanation:

civilizations developed around rivers because their waters provided places to hunt and fish. also, as the rivers flooded, the lands around them became fertile. this allowed them to support farming. this is especially true of the nile river, which flooded the same time each year.