Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.
Q: Originating in Germany, the Danube flows southeast for 2,860 km (1,780 mi), passing through or touching the border of Austria, Slovakia, Hungary, Croatia, Serbia, Romania, Bulgaria, Moldova and Ukraine before emptying into the Black Sea.
A:
What body of water does Danube join?