Answer: Metaphor .
Step-by-step explanation:
This is a line from Martin Luther King Jr.'s open letter, known as The Letter from Birmingham Jail, in which he supports nonviolent resistance to racial discrimination.
King describes all the hardships that people face, and explains that for people who have never experienced them, it is easy to say that those who did need to wait patiently for their rights. One of these hardships is segregation, and King uses a metaphor in this line to emphasize it.
A metaphor is a figure of speech in which two objects/concepts that do not have much in common are compared, in order to explain an idea. There is no such thing as "stinging darts of segregation", but King uses sharp darts to demonstrate the effect that racial discrimination has on people who experience it.