sentences:  Ritzen also worked as a distinguished visiting professor at the Robert M. La Follette School of Public Affairs of the University of Wisconsin-Madison from February 1988 until November 1989.After the election of 1989 Ritzen was appointed as Minister of Education and Sciences in the Cabinet Lubbers III, taking office on 7 November 1989.In January 1994 Ritzen announced that he would not stand for the election of 1994.