Question: In what century was the the style of voices popular that the Liebeslieder Walzer, Op. 52 was in?
Sentence (from "Liebeslieder Walzer (ballet)"): Liebeslieder Walzer is a ballet by New York City Ballet co-founder and ballet master George Balanchine, based on the Brahms' "Liebeslieder Walzer", Op. 52, and their sequel "Neue Liebeslieder", Op. 65.
Relevant evidence: No