The significant aspect of the dates when Lincoln's speech and King's letter were written lies in the historical context of racism in America. King intentionally wrote his letter one hundred years after Lincoln's speech to highlight the ongoing injustices faced by Black citizens. This parallel underscores that, despite the progress symbolized by the Emancipation Proclamation, systemic racism and inequality persisted in American society a century later. Therefore, the most accurate answer is:
King intentionally wrote his letter one hundred years after Lincoln's speech to draw attention to the ongoing injustices Black citizens faced.