The correct answer to this open question is the following.
Although there are no options attached we can say the following.
The three details which support the claim that “MLK was the most significant civil rights leader during the civil rights movement," are the following.
1.- Dr. Martin Luther King led the Montgomery Bus Boycott that started on December 5, 1955.
2.- Dr. Martin Luther King wrote the important document titled "Letter's Fron a Birmingham Jai," in which he explained his non-violent approach.
3.- DR. Martin Luther King was the author of the famous speech "I Had a Dream," which is considered to be one of the most inspirational speeches in the history of the United States.
We also can add that on January 10, 1957, Dr. Martin Luther King became the first President of the Southern Christian Leadership Conference (SCLC), whose headquarters were in Atlanta, Georgia.
Dr. King was the most important leader of the Civil Rights movement in the South of the United States, and an inspiration for millions of African American people and other minority groups.