Monteverdi: L'Orfeo, favola in musica, SV 318, Act 4 - Monteverdi: L'Orfeo, favola in musica, SV 318, Act 4: "Ma mentre io canto" (Orfeo) (奥菲欧，作品318号，第四幕 - 但是，尽管我唱（奥菲欧）)