The correct option is D Serbia, Bulgaria, Greece, Croatia and Romania
The Balkans, which
was a serious source of nationalist tension in Europe after 1871, was a
region comprising of Romania, Bulgaria, Albania, Greece, Macedonia, Croatia, Bosnia-Herzegovina,
Slovenia, Serbia and Montenegro whose inhabitants were broadly known as the
Slavs. Balkans were under Ottoman Empire, one by one disintegrated and declared
independence which led to nationalistic tension in Europe.