Following Archduke Franz Ferdinand's assassination, Austro-Hungarian leaders:

A. aided the Ottoman Empire in its campaign to keep Serbia under its control.

B. executed nearly all prominent Serbs living in Austria-Hungary

C. threatened to invade Serbia if Serb leaders did not agree to a set of strict demands.

D ... formed an alliance with Great Britain to protect Austria-Hungary from future attacks.

The answer is threatened to to invade Serbia If SErb leaders did not agree to a set of strict demands

Explanation:

The answer is C

The correct answer is B.

On June 28, 1914, the assassination of Archduke Franz Ferdinand, heir to the Austro-Hungarian Empire, at the hands of a Serbian-led Bosnian nationalist group took place in Sarajevo (then part of the Austro-Hungarian Empire).

The Austro-Hungarian authorities encouraged a series of anti-Serb riots in Sarajevo, in which Croats and Bosnians murdered two people of Serbian origin and damaged numerous Serbian-owned buildings, and violent actions were organized against Serbs outside Sarajevo and in the city were produced more than a hundred arrests of suspects of having participated in or assisted in the assassination of the Archduke; the attacks spread to other large cities of the Austro-Hungarian Empire in present-day Bosnia, Croatia and Slovenia. The authorities imprisoned or extradited around 5500 prominent Serbs throughout Bosnia, of whom between 700 and 2200 died in prison. More than 460 Serbs were sentenced to death and a special militia of Bosnian majority known as Schutzkorps began to persecute the Serbs systematically.