(A) Italy
(B) Britain
(C) Austria-Hungary
(D) ** Russia
EXPLANATIONS BELOW
Concept note-1: -Austria-Hungary declares war on Serbia On 28 July, Austria-Hungary declared war on Serbia. It was determined to take decisive action against Serbia and, by now, knew this risked war with Russia, Serbia’s supporter.
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: -Over 30 nations declared war between 1914 and 1918. The majority joined on the side of the Allies, including Serbia, Russia, France, Britain, Italy and the United States. They were opposed by Germany, Austria-Hungary, Bulgaria and the Ottoman Empire, who together formed the Central Powers.