The correct answer to this question is D. The SCLC (which stands for Southern Christian Leadership Conference) was formed in the aftermath of the succesful bus boycott that happened in Montgomery in 1955 and 1956. The SCLC was not formed immediately after the boycott, but there were only a few months separating the end of the boycott and the official creation of the SCLC.
There were at least two major reasons for the founding of the SCLC. First, most of the organizations that were in existence at the time were based in the North. The SCLC leaders wanted to create a Southern organization. Second, the existing organizations were secular. By contrast, the SCLC was explicitly a church-based organization.
After the bus boycott, various leaders, including Dr. King created the SCLC to push for civil rights in a Southern and Christian way. Therefore, the right answer is D.
The Southern Christian Leadership Conference formed as a result of the Montgomery Bus Boycott. This was an organization of African-American ministers. They saw how effective the nonviolent approach worked with the Montgomery Bus Boycott. Thus, they formed this group to work to end segregation in the South using nonviolent methods.
The National Association for the Advancement of Colored People had been in existence and had been active for many years prior to the Montgomery Bus Boycott. For example, the NAACP was involved in the Brown v Board of Education case in 1954.
The Congress of Racial Equality formed in the 1940s. James Farmer created it. This group used nonviolent methods such as the sit-in to work to end segregation.
The Student Nonviolent Coordinating Committee formed in 1960 to work to try to end segregation. This was a group that included students. They used nonviolent methods of protest such as the sit-in to try to end segregation.
Thus, the correct answer to your question is answer D. The Southern Christian Leadership Conference formed in 1957 as a result of the success of the Montgomery Bus Boycott.