@book { BusreisenimKontextdesnachhaltigenTourismus,
    title = "Busreisen im Kontext des nachhaltigen Tourismus",
    author = "Iris {Kern}",
    year = "2011",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783656007067",
    url = "https://www.hausarbeiten.de/document/178590"
}