The king used the allusion to suggest the moral significance of his cause.
The correct option is C.
Martin Luther King Jr. was a Baptist minister and activist.
He was the most recognizable voice and leader in the civil rights movement.
He advanced the civil rules for black people in the United States.
Furthermore, he was inspired by the non-violence activism of Mahatma Gandhi.
Thus, the correct option is C, to propose the moral significance of his cause.