Based on the information provided, the reader can infer that the impact of the Emancipation Proclamation is best represented by option A: It provided hope but did not completely end oppression. This is supported by the quote "But one hundred years later, the Negro still is not free," indicating that while the Proclamation was a significant step towards freedom, it did not eliminate all forms of oppression faced by African Americans.
For the second part of your question, the quote that supports the key idea that the Emancipation Proclamation was significant is C: This momentous decree came as a great beacon light of hope. This quote highlights the Proclamation's importance by describing it as a source of hope for millions of enslaved people, thus reinforcing its significance in American history.