Final answer:
The central idea of this speech is that America is constantly refining and improving its commitment to its ideals of freedom and equality.
Step-by-step explanation:
The central idea of this speech is that America is constantly in a process of refining and improving its commitment to its ideals of freedom and equality (option B). The speech discusses the history of racism in America and the ongoing fight for racial justice, highlighting how racism has been deeply ingrained in American society. It emphasizes the importance of unity and fighting against racism as a team, and the need for education, culture, and liberty as essential tools to overcome racism.