Which of the following best states the central idea of the passage？

A. The Byzantine Empire was a unique case in which the usual order of military and economic revival preceding cultural revival was reversed.
B. After 810 Byzantine economic recovery spurred a military and, later, cultural expansion that lasted until 1453.
C. The revival of Byzantine learning is an inexplicable phenomenon, and its economic and military precursors have yet to be discovered.
D. The revival of the Byzantine Empire shows cultural rebirth preceding economic and military revival, the reverse of the commonly accepted order of progress.