@book { DiesozialenEffektevonNachhilfe,
    title = "Die sozialen Effekte von Nachhilfe",
    author = "Marion {Biroth}",
    year = "2009",
    publisher = "GRIN Verlag",
    address = "München, Germany",
    doi = "10.3239/9783640257683",
    url = "https://www.hausarbeiten.de/document/121258"
}