There are two hints that point towards option A: the line is drawn over the sea, which means that it refers to a path over the sea, and not to any territory or kingdom. The second one is the fact that the route begins and ends in Venice.
Venice (and to a lesser extent, Genoa) had a monopoly on trade from the Italian Maritime Republics from the 12th century onwards. These routes connected the Mediterranean and the rest of Europe with the "Orient." Europe traded wine, metal and oil in exchange for goods such as silk, salt and spices.
