Part A
The correct answer is: B. Black Americans have been excluded from economic prosperity.
The details in paragraphs 3-4 highlight the ongoing struggles faced by Black Americans, such as living in poverty and enduring segregation and discrimination, which supports this idea.
Part B
The best supporting quote is: C. One hundred years later, the Negro lives on a lonely island of poverty in the midst of a vast ocean of material prosperity. (paragraph 3)
This quote directly illustrates the exclusion of Black Americans from the economic prosperity that surrounds them, emphasizing their ongoing struggles.