(A) start of the civil war in Russia
(B) sinking of the British liner, Lusitania
(C) ** assassination of the heir to the throne of the Austro-Hungarian Empire
(D) attack on Poland by the German army
EXPLANATIONS BELOW
Concept note-1: -The assassination of Franz Ferdinand is considered the most immediate cause of World War I. After his death, Archduke Karl became the heir presumptive of Austria-Hungary.
Concept note-2: -The immediate cause of World War I that made the aforementioned items come into play (alliances, imperialism, militarism, nationalism) was the assassination of Archduke Franz Ferdinand of Austria-Hungary. In June 1914, a Serbian-nationalist terrorist group called the Black Hand sent groups to assassinate the Archduke.
Concept note-3: -The assassination of Archduke Franz Ferdinand was the immediate cause of a war between two great powers-Russia and the Habsburg Austro-Hungarian Empire.
Concept note-4: -The political objective of the assassination was to free Bosnia and Herzegovina of Austria-Hungarian rule and establish a common South Slav ("Yugoslav") state. The assassination precipitated the July Crisis which led to Austria-Hungary declaring war on Serbia and the start of World War I.
Concept note-5: -The start of World War I, the so-called “Great War” of 1914 to 1918, was triggered when a teenage Serbian revolutionary shot Archduke Franz Ferdinand, the presumptive heir to the Austro-Hungarian throne, and his wife Sophie on their visit to the Bosnian capital of Sarajevo.