@book { UnterrichtsformenimOffenenUnterricht,
    title = "Unterrichtsformen im Offenen Unterricht",
    author = "Maria {Enderlein}",
    year = "2007",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783638818827",
    url = "https://www.hausarbeiten.de/document/76917"
}