(A) a treaty.
(B) a contract.
(C) an ultimatum.
(D) ** an alliance.
EXPLANATIONS BELOW
Concept note-1: -Germany’s Otto von Bismarck saw the alliance as a way to prevent the isolation of Germany and to preserve peace, as Russia would not wage war against both empires.
Concept note-2: -Triple Alliance, secret agreement between Germany, Austria-Hungary, and Italy formed in May 1882 and renewed periodically until World War I. Germany and Austria-Hungary had been closely allied since 1879. Italy sought their support against France shortly after losing North African ambitions to the French.
Concept note-3: -Broader European war ensued because German political and military figures egged on Austria-Hungary, Germany’s ally, to attack Serbia. This alarmed Russia, Serbia’s supporter, which put its armies on a war footing before all options for peace had been fully exhausted.
Concept note-4: -The war extended and changed these two sides. Germany and its allies were known as the Central Powers: Germany and Austria-Hungary, later joined by the Ottoman Empire (Turkey plus the Middle East) and Bulgaria.