Why was Prince Henry considered a visionary? He sailed for the King of Portugal exploring the coast of Africa.
His determination led to new educational methods for navigation.
He claimed new lands along the African coast.
He was the explorer who finally discovered the water route to Asia.

yup! you are correct it is b.

the conditions that made the byzantine empire vulnerable to attacks by the muslin turks were the sack of constantinople by western crusaders, the conquests of the sultanate of rum, presence of rival kingdoms and finally the set up of fiefdoms at the empire which were owned by the ghazis (turkish warriors).

the viking voyages took place during the middle ages, which was about this time. 500 to 1350. the viking voyages took place during the middle ages, which was about this time.