The correct answers are B, C and E.
The Ku Klux Klan (KKK) was an organization of white supremacists that emerged in the US in the late 1960s, hence in the post Cilvil War era, also called Reconstruction period. It lost strenght during the 1970s and flourished again the mid-1920s.
KKK aimed to stop the actions undertaken by African American leaders in the South and to prevent black citizens from exercising their voting rights and other civil rights that they were granted by the 14th and 15th Amendments to the US Constitution.