Answer:
C. They carried out mass executions.
D. They were known as mobilized killing units.
E. They were used by Germany during the invasions of Poland and the Soviet Union.
Explanation:
Einsatzgruppen was founded in 1939 as a mobile death killing unit (squad) of the Nazi German security forces during the second world war (the invasion of the Soviet Union in 1941 and Poland in 1931). The Einsatzgruppen were mainly part of the Schutzstaffel paramilitary and as such played a significant role in the mass murder of the Jewish people, Romanis, priesthood members and the intelligentsia in Poland.
Hence, the statements which best describe Einsatzgruppen are;
I. They carried out mass executions.
II. They were known as mobilized killing units.
III. They were used by Germany during the invasions of Poland and the Soviet Union.
