Using 'der' / 'den' without noun? Connecting sentences..
Entlang von Baden-Württembergs Westgrenze fließt der Rhein, (der / den / die) 1.320 Kilometer lang ist.
Which one is it, and why? I have looked it up in several grammar books and cannot find a solution? Also, so I can practice further, what is this situation referred to in grammar.