Final answer:
The immediate cause of World War I was the assassination of Archduke Franz Ferdinand of Austria by Serbian nationalist Gavrilo Princip, which triggered a sequence of declarations of war due to existing alliances among the European powers.
Step-by-step explanation:
The assassination of Archduke Franz Ferdinand of Austria was the immediate cause of World War I. On June 28, 1914, Gavrilo Princip, a young Serbian nationalist, assassinated the archduke and his wife during their visit to Sarajevo. This event set off a chain reaction among the European powers, leading to the full-scale outbreak of the war.
The assassination led to a series of demands from Austria-Hungary to Serbia, which were not fully met. As a result, Austria-Hungary, with the backing of Germany, declared war on Serbia. Russia, bound by a treaty with Serbia, entered the war against Austria-Hungary, followed by Germany declaring war on Russia and France. Great Britain, allied with France, subsequently declared war on Germany, thus escalating the conflict into a global war. The intricate web of alliances and the rise in nationalism and militarism among the European powers contributed to the rapid expansion of the war.
The correct answer to the question is option c. Archduke Francis Ferdinand of Austria.