The correct answer is C) Alliances forced many countries to go to war in support of either Austria-Hungary or Serbia.
The assassination of Archduke Franz Ferdinand by a Serb lead to World War I in that "Alliances forced many countries to go to war in support of either Austria-Hungary or Serbia."
On June 28, 1914, Archduke Franz Ferdinand and his wife Sophie were assassinated in Sarajevo. The Archduke had planned a trip to Sarajevo to oversee the Austrian-Hungary troops established in that region. The assassination increased tension in central Europe and the incident was one of the reasons that started World War 1.