Serbia Became Essentially Independent of the Ottoman Empire in 1805

Serbia became essentially independent of the Ottoman Empire in 1805

A) because the Ottoman Empire was busy suppressing the Greek uprising.
B) but it was reabsorbed two decades later.
C) after Russian threats prevented the Ottomans from disarming Serbians following a Janissary revolt.
D) because Mohammad Ali recalled the Janissaries to Egypt.
E) by assassinating Archduke Franz Ferdinand.