Final answer:
The paragraph from 'A Quilt Of A Country' emphasizes that despite its profound diversity and occasional intergroup tensions, America remains united as one nation, not divided into separate countries.
Step-by-step explanation:
The central idea of the excerpt from "A Quilt Of A Country" is summarized in option B. America is a united country despite its cultural differences. The paragraph discusses the paradox of a nation that is profoundly diverse and at times appears to be at odds with itself, yet remains united as one country. This unity persists despite the cultural tensions and contradictions that might lead to divisions in other countries. The quoted text underscores the impossibly interwoven nature of American society which, through its diversity and cultural mosaic, forms a single nation rather than splintering into separate entities.