The correct answer is - Danube.
None of the suggested rivers passes through 13 countries, but the Danube is the closest to that.
The Danube River is the second largest river in Europe, after Volga, and it is 2850 km long.
The river starts in the Black Forest in Germany, and ends in the Black Sea.
The Danube River passes through or touches the borders of 10 countries in total, starting in Germany, than Austria, Slovakia, Hungary, Croatia, Serbia, Romania, Bulgaria, Moldova, and Ukraine.
