The correct answer is - B. Access to Russia's economic markets.
Eastern Europe enjoys an economic advantage because it has access to the Russian economic markets. Russia is one of the richest countries in the world with natural resources, some of which are essential for the functioning of pretty much of every country in the modern world, such as the oil and gas. Because Russia is abundant with these natural resources, the fact that Eastern Europe is bordering it, gives it an advantage because they are much easier to access, and also, Russia is a country that in general gives the best offers on the global market when we speak about natural resources.