context: It takes its source in the Black Forest mountains in Germany. The Danube flows through the territory or is the border of ten states: Germany, Austria, Slovakia, Hungary, Croatia, Serbia, Bulgaria, Romania, Ukraine and Moldova; passes through such capitals of Central and Southeast Europe as Vienna, Bratislava, Budapest and Belgrade [1]. In addition to these ten countries, in the Danube basin there are certain territories of another nine European states [1]. The river flows into the Black Sea, forming a delta on the border of Romania and Ukraine; the Romanian part of this delta is listed as a UNESCO World Heritage Site [2].
question: How many capitals does the Danube cross?
answers.text: Vienna, Bratislava, Budapest and Belgrade