Why Did the Vikings Fail Spectacularly When They Attacked Constantinople

Why did the Vikings fail spectacularly when they attacked Constantinople?

A) Their supply lines were overextended and they soon began to starve.
B) The city was landlocked, so the Vikings had to leave their ships to besiege the city.
C) They faced, for the first time, a city defended by well-engineered late Roman walls and Greek fire.
D) The slaves the Vikings were bringing to sell in Constantinople rose up and joined the Byzantine side.