Answer:
c. was countered by the Byzantine usage of a new weapon, "Greek fire."
Step-by-step explanation:
"Greek Fire" consisted in burning an enemy ship by throwing fire from a flame-throwing weapon from another ship.
This Greek Fire was first used by the Byzantines in 673. It is called Greek Fire because the Byzantine Empire was largely Greek-speaking.
The Greek Fire was used effectively in two naval battles against muslims invations in the 8th century. This victories helped Constantinople survive and remain in Byzantine (Christian) control.