To investigate the reason the assassination of Archduke Franz Ferdinand sparked World War I, the most relevant option from the list provided is the nationality of Archduke Franz Ferdinand’s assassin. The assassin was a Bosnian Serb nationalist, and his actions were tied to the tensions between Austria-Hungary and Serbia, which contributed to the outbreak of the war.
While the other options may provide context about the war or the alliance system, they do not directly relate to the immediate cause of the war stemming from the assassination.