The correct answer is C.
King's "Letter from Birmingham Jail," was a response a to letter published in a newspaper decrying the demonstrations for which he had been incarcerated and calling them "unwise".
In this letter, King explains what these protests in Birmingham were about and why it was necessary for him and his fellow protestors to fight for their rights, since no one, not the local leaders or the courts, would confront the issues at hand.
The best answer is "when you are making an observation." While writing an autobiography, you are describing events in your past. If you are observing something, you must distinguish these insights and conclusions from the timeline of events you have been describing. The simplest comparison is to imagine you are watching a movie, the story is progressing, and then the narrator stops, looks at the camera, and says, in the present, his or her observation about what is happening. These observations are happening at a different time from the events of the narrative and therefore are described in the present.
