Q. Which one of the following was the "immediate cause" or the "spark" for the start of World War I?
Answer: Assassination of Archduke Franz Ferdinand of Austria-Hungary.
Notes: The immediate cause of World War I was the assassination of Archduke Franz Ferdinand of Austria-Hungary. In June 1914, a Serbian nationalist Gavrilo Princip assassinated Archduke and his wife to take revenge against the occupation of Bosnia-Herzegovina by Austria-Hungary. immediately, after the assassination, Austria-Hungary declared the war over Serbia. This further leads to alliance nations declaring war between themselves, caused WW I.