It is A) The assasination of Archduke Francis Ferdinand and his wife caused uproar and the killings sparked a chain of events that led to the outbreak of World War I by early August. Basically Austria blamed Serbia (where this had happened) for deliberately instigating their murder because it was done by a nationalist.Austria asked for assurances that Germany would step in on its side against Russia and its allies, including France So later Austria-Hungary declared war on Serbia causing World War 1