sentences:  Zijlstra worked as a researcher at the Rotterdam School of Economics from December 1945 until January 1947 and as an associate professor of Public economics at the Rotterdam School of Economics from 1 January 1947 until 8 July 1948 when got a doctorate as an Doctor of Philosophy in Public economics.Zijlstra worked as a professor of Public economics at the Free University Amsterdam from 28 October 1948 until 2 September 1952.After the election of 1952 Zijlstra was appointed as Minister of Economic Affairs in the Cabinet Drees II, taking office on 2 September 1952.