Answer: I. their sublime courage
II. their willingness to suffer
III. their amazing discipline in the midst of great provocation
Explanation: A sit in is an organized non-violent protest demonstration in which participants seat themselves in a place and refuse to move. Martin Luther King Jr. and his fellow protesters were arrested and sent to jail for a sit in protesting segregation in Birmingham, Alabama. After reading an open letter from eight white clergymen in the local newspaper criticizing him and his fellow activists, he decided to write back to let them know what was on his mind.
The letter defends the strategy of nonviolent resistance to racism. It pointed out that people have a moral responsibility to break unjust laws and take direct action rather than waiting potentially forever for justice to come through the courts.
Furthermore, he wrote that he wished the protesters had been commended for the three reasons above and that despite provocation, the protests never turned violent.