The correct answer is - D. cultural.
Once the empire was divided, and the Eastern Roman Empire became stronger and stronger, and surpassed the power and influence of the Western Empire, Its capital, Constantinople was becoming hugely important city in the regional scene, and started taking the spot as the greatest city of its time. It became a military superpower, reformed politics and managed to have big influence on the politics in the region, and economically it was extremely well situated. But one thing was never recognized to this great city, and that was the cultural aspect, and it always remained in the shadow of the culture that was spread out and promoted by Rome.