B. SS believed in Nazi rhetoric about Aryan superiority.
The SS (Schutzstaffel) was a paramilitary organization in Nazi Germany that was responsible for many of the regime's worst atrocities, including the Holocaust. Members of the SS were fervent believers in Nazi ideology, including the notion of Aryan racial superiority and the need to eliminate Jews and other "undesirables" from German society. The Einsatzgruppen, which were mobile killing squads that operated in Nazi-occupied territories, were staffed largely by SS members precisely because of their ideological commitment to the Nazi cause. SS members were also trained in military tactics and were accustomed to carrying out orders without question, making them particularly effective at carrying out the mass murder of civilians. Therefore, it makes sense that most of the members of the Einsatzgruppen were SS.