The correct answer is C) the Ku Klux Klan.
The group that would have opposed the passage of the Reconstruction Amendments was the Ku Klux Klan.
On December 24, 1865, former Confederate veterans from Pulaski, Tennessee formed the Ku Klux Klan. That was the time of the Reconstruction of the Southern states after the Civil War. The KKK is characterized for its anti-immigration ideas, white race supremacy, and nationalism. This organization would have opposed the passage of the Reconstruction Amendments, that ended slavery and supported the rights of black people.