(A) Germany
(B) Russia
(C) Slovakia
(D) ** Serbia
EXPLANATIONS BELOW
Concept note-1: -When it was learned that the heir-apparent to the Austrian throne, Franz Ferdinand, was scheduled to visit Sarajevo in June of 1914, the Black Hand decided to assassinate him because of his perceived threat to Serbian independence.
Concept note-2: -In 1914, Apis allegedly decided that Archduke Franz Ferdinand, the heir-apparent of Austria, should be assassinated, as he was trying to pacify the Serbians, which would prevent a revolution if he was successful. Towards that end, three young Bosnian Serbs were allegedly recruited to kill the Archduke.