Which of the following was NOT a cause for the decline of the Ottoman Empire?

a.Oppressive demands of local officials caused the peasantry to abandon their holdings and flee.
b.The ability of individual sultans to rule declined.
c.The addition of European military technology such as light artillery made the Janissaries so powerful that they could challenge the authority of the sultan.
d. Local officials began to retain increasing amounts of revenue for their own purposes.