(A) ** Russia
(B) Germany
(C) France
(D) Britian
EXPLANATIONS BELOW
Concept note-1: -Austria knew that conflict with Serbia would likely involve Russia, which saw itself as Serbia’s protector. Austria-Hungary turned to its own ally. On 5 July, Germany promised Austria full support for a severe response against Serbia.
Concept note-2: -Although Russia had no formal treaty obligation to Serbia, it stressed its desire to control the Balkans and had a long-term perspective toward gaining a military advantage over Germany and Austria-Hungary in the region.
Concept note-3: -On July 28, 1914, one month to the day after Archduke Franz Ferdinand of Austria and his wife were killed by a Serbian nationalist in Sarajevo, Austria-Hungary declares war on Serbia, effectively beginning the First World War.