Answer:
The correct answer is C. Radical Republicans lost power in Congress for all of the following reasons except that all the goals of the Radical Republicans had been achieved by 1876.
In reality, Reconstruction ended early in 1876 as a result of a political negotiation between Republicans and Democrats, whereby Republicans were given control of the federal government, in exchange for their withdrawal from the southern territories and their return to the democratic politicians. Thus, despite the fact that there were still many political, economic and social projects to be developed in the region, in 1876 the South was demilitarized and the Democrats returned to power, ending the Reconstruction.