Based on their views and preferences, the most suitable organizations for Robert and Carol would be:
Robert likely joined the National Association for the Advancement of Colored People (NAACP), which focused on improving social, political, and economic opportunities for African Americans and often engaged in letter-writing campaigns and legal challenges.
Carol likely joined the Student Nonviolent Coordinating Committee (SNCC), which was known for organizing sit-ins and direct action protests, including the focus on enforcing civil rights as articulated in cases like Brown v. Board of Education.
Thus, the correct answer is:
C. Robert likely joined the National Association for the Advancement of Colored People and Carol likely joined the Southern Christian Leadership Conference.