 Complete the following phrase:  The liquidation of WWII ghettos across Poland was closely connected with the formation of highly secretive killing centers built by various German companies including I.A. Topf and Sons of Erfurt, and C.H. Kori GmbH. Jews were deported from the Warsaw Ghetto alone to Treblinka extermination camp over the course of 52 days during Grossaktion Warsaw 1942. In some of the ghettos the local resistance organizations launched the ghetto uprisings; none were successful, and the Jewish populations of the ghettos were almost entirely Jews from Eastern Poland areas now in Lithuania, Belarus, Ukraine were killed using guns rather than in gas chambers, see 