D. Poverty isolates African Americans from the mainstream of American society.
Explanation:
This is the statement that best describes the meaning of the excerpt. In these lines, the author presents an image of isolation when it comes to African Americans. We learn that African Americans are on an "island" which is surrounded by material property. The implication is that African Americans as a group are poorer than other groups in society, and that this isolates them in the same way as if they were located on an island.