Final answer:
The country with the Black Sea to the south feeding the Sea of Marmara via the Bosporus is Turkey, a nation straddling two continents with historical significance as the core of the Ottoman Empire.
Step-by-step explanation:
The country that has the Black Sea in the southern extension and feeds the Sea of Marmara via the Bosporus is Turkey. Turkey plays a significant geographical and historical role as it bridges two continents, Europe and Asia.
The Bosporus is the strategic waterway that separates the Asian part of Turkey from its small European section on the western side.
Historically, Turkey was the heartland of the Ottoman Empire, which exerted substantial influence over the region's maritime routes, including those connecting the Black Sea to the Mediterranean.
Today, Turkey is known for its vibrant city of Istanbul (formerly Constantinople), which straddles the Bosporus, solidifying its unique presence in both continents.