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1.
Cologne is the biggest city on the Rhine.
It is with ~1.086.000 Inhabitants, followed by Rotterdam with ~646.000 and Dusseldorf with ~619.000 Inhabitants.
2.
The Seine is the longest river in France.
The longest river in France is the Loire.
3.
Switzerland is the only country in Europe that has tributaries leading to the North Sea, the Mediterranean and the Black Sea.
See these examples: the Rhine flows to the North Sea, the Rhone to the Mediterranean and the Inn (a tributary river of the Danube) into the Black Sea.
4.
Germany's eastern border with Poland are the rivers Oder and Elbe.
Oder and Neisse, not Oder and Elbe.
5.
All of Ukraine's rivers lead into the Black Sea.
Bug river begins in Ukraine and joins the Vistula, that flows into the Baltic Sea.
6.
All of Hungary's rivers lead into the Black Sea.
All of its rivers are tributaries of the Danube and therefore lead into the Black Sea.
7.
Norway's Fjords are considered rivers.
They are not.
8.
Parts of the Borders of Switzerland, Liechtenstein, Germany, France and Luxembourg follow the Rhine.
Luxembourg doesn't lie on the Rhine.
9.
Tiber, Thames and Tajo are rivers that flow through European capital cities.
Tiber (Rome), Thames (London), Tajo (Lisbon)
10.
The Danube is the only river that flows through four capital cities.
Vienna, Bratislava, Budapest, Belgrade