Assassination of Archduke was the event that sparked the outbreak of World War I. The correct option among all the options given in the question is option "4". The assassination of Archduke Franz Ferdinand occurred on 28th July of the year 1914. Franz Ferdinand was the heir to Austro Hungarian Empire and he was shot dead along with his wife by Gavrilo Princip in Sarajevo. Gavrilo was a Bosnian Serb nationalist. This incident is considered the main reason behind the outbreak of the first world War. The war left around 17 million dead and about 20 million people wounded.