The Wagner tuba, a modified member of the horn family, appears in Richard Wagner's cycle Der Ring des Nibelungen and several other works by Strauss, Béla Bartók, and others; it has a prominent role in Anton Bruckner's Symphony No. 7 in E Major. Cornets appear in Pyotr Ilyich Tchaikovsky's ballet Swan Lake, Claude Debussy's La Mer, and several orchestral works by Hector Berlioz. Unless these instruments are played by members doubling on another instrument (for example, a trombone player changing to euphonium for a certain passage), orchestras will use freelance musicians to augment their regular rosters.
Try to answer this question if possible (otherwise reply "unanswerable"): Which symphony of Anton Bruckner's does the Wagner tuba have a prominent role in?
Symphony No. 7 in E Major