I am pretty sure the awnser is B the collapse of communism
Humans tend to congregate and form settlements around areas that are rich with natural resources such as forests and rivers, because these locations support life and the economy.
The general trend of the European population is: declining. This is due to a number of factors, the most important of them is the negative population growth: women are having less than 2 children (currently 1.6 children). and 2.2 children per woman are needed to keep the population size stable
