Africa is the 7th biggest
Communicate with other peope
This policy was called "containment" - the idea was to contain communism from spreading to new countries without trying to actively challenge the communist system in the countries that already had it.
This policy lead to some proxy wars, in which the US fought the Soviet Union for the free countries.
The best anwer is 4); vegetation is vital from keeping a place from becoming a desert. It transforms the ground into that with more nutrients, captures water and stops erosion, as well as protects the nutrient parts of the soil from being carried away with the wind.
