Read the excerpt from Martin Luther King Jr.'s "I Have a Dream" speech. But one hundred years later, the Negro still is not free. One hundred years later, the life of the Negro is still sadly crippled by the manacles of segregation and the chains of discrimination. One hundred years later, the Negro lives on a lonely island of poverty in the midst of a vast ocean of material prosperity. One hundred years later, the Negro is still languished in the corners of American society and finds himself an exile in his own land. And so we’ve come here today to dramatize a shameful condition.
What is the allusion in this excerpt?

Dr. King alludes to America as a land of equal opportunity.
Dr. King alludes to the horrors of bondage and enslavement.
Dr. King alludes to Lincoln's freeing of enslaved people.
Dr. King alludes to the Founding Fathers and America's core values.