Find the borders between two countries that occur more than once. They are separated in two sections: those which are repeated even without considering enclaves, and those which are repeated only if you consider enclaves.
Data from http://en.wikipedia.org/wiki/List_of_countries_and_territories_by_land_borders adapted to countries present in 'Countries of the World' quiz
Colour clues: borders that are at least triple (without considering enclaves) are highlighted