Read the excerpt from Martin Luther King Jr.'s "I Have a Dream" speech. Five score years ago, a great American, in whose symbolic shadow we stand today, signed the Emancipation Proclamation. This momentous decree came as a great beacon light of hope to millions of Negro slaves who had been seared in the flames of withering injustice. It came as a joyous daybreak to end the long night of their captivity.
What is the allusion in this excerpt?

Dr. King alludes to America as a land of equal opportunity.
Dr. King alludes to the Founding Fathers and America's core values.
Dr. King alludes to the recent achievements of the civil rights movement.
Dr. King alludes to the wording Lincoln used in the Gettysburg Address.