Bosnia and Herzegovina are bordered by three countries. To the south lies Montenegro, to the east lies Serbia, and to the north and west are Croatia.
Romania has borders with Hungary, Serbia, Bulgaria, Moldova and Ukraine.
Romania borders Bulgaria, Serbia, Hungary, the Ukraine, and Moldova.
Hungary, Serbia, Bulgaria, Moldova, Ukraine (and the Black Sea).
No country borders both Belarus and Serbia.
The Danube runs through Germany, Austria, Hungary and Serbia. It borders Part of Serbia and Croatia, Hungary and Slovakia, and Romania and Bulgaria.
Not four, but five countries ! Bulgaria Moldavia Ukraine Hungary Serbia Black Sea
Hungary, Serbia, Bulgaria, Moldova, Ukraine and the Black Sea.
Macedonia shares its borders with Serbia, Albania, Greece and Bulgaria
Serbia
Montenegro is surrounded by Croatia, Bosnia Herzegovina, Serbia (plus the unrecognized independent province of Kosovo) and Albania. The western coast of Montenegro borders the Adriatic Sea across which is Italy.
The region, Bosnia, borders the countries of Croatia, Serbia, and Montenegro and is landlocked. However, if you mean the country Bosnia & Herzegovina, then it also borders the Adriatic Sea.
Romanian borders are with: Moldova, Ukraine, Hungary, Serbia, Bulgaria and the Black Sea.