Final answer:
Sentence 3, "Malcolm X is a Negro," does not belong in the paragraph as it is out of context and does not support the central theme of the passage from Martin Luther King Jr's "I Have a Dream" speech.
Step-by-step explanation:
The sentence that does not belong in the paragraph from Martin Luther King Jr's "I Have a Dream" speech is sentence marked 3: "Malcolm X is a Negro." This sentence does not fit with the rest of the paragraph, as it introduces a different person and shifts the focus away from the Emancipation Proclamation and the plight of the Negro slaves.
This sentence is out of context and does not contribute to the flow or the central theme of the paragraph, which deals with the historical impact of the Emancipation Proclamation and the continued struggle for freedom and equality by African Americans one hundred years later. Unlike the other sentences, it neither elaborates on the historical significance of the Emancipation Proclamation nor on the state of racial injustice contemporaneous to King's speech.