The correct answer is Northerners were growing increasingly hostile to President's Johnson and no longer wanted to support his agenda.
That was not a reason the North began to lose interest in the southern reconstruction by the early 1870s.
All the other options were reasons why the North lost interest in the South's reconstruction. The many mentioned problems dissuaded Northerners to participate in the reconstruction effort of the much destroyed South after the Civil War. Furthermore, the North thought that it was time for the South to assume their responsibility. President Lincoln had given the southern states leeway to do Reconstruction at their own pace while radical Republicans demanded severe punishments for their acts in war
The other options of the question were A) Southern intransigence was increasingly frustrating to the North, whose soldiers had fought for black's freedom. C) other issues, such as the Indian Wars, western expansion, and others started to overtake Northerner's attention. D) real and propagandized evidence of corruption in the Reconstruction Southern governments discouraged the North.