Edited sentence: After WW II Poland had just one house of Parliament (Sejm).Edward Osobka-Morawski was Poland's prime minister between 1945 and 1947.In the sentence "... students' march which took place in March 1968", "march" could be changed to "demonstrations".It is indicated Mazowiecki was "in the Sejm (the Polish Parliament's lower house" 1961-72.Poland's Senat was established at the end of communist dictatorship in 1989.Technically he was not a communist since he was a member of the Polish Socialist Party (PPS) at this time.There were non-communist prime ministers in Hungary, Romania and perhaps Bulgaria prior to 1948 as well.To say Mazowiecki was "first non-communist prime minister in Central and Eastern Europe after WW II" is not realy correct