http://www.hueber.de/shared/uebungen/themen-aktuell/lerner/uebungen/fset.php?Volume=1&Lection=9&Exercise=5&SubExercise=1

http://www.mein-deutschbuch.de/lernen.php?menu_id=165

http://www.education.vic.gov.au/languagesonline/german/sect31/no_06/no_06.htm

http://www.education.vic.gov.au/languagesonline/german/sect31/no_07/no_07.htm

http://www.education.vic.gov.au/languagesonline/german/sect31/no_10/no_10.htm