Correct Option: D

The First World War involved all the world’s great powers, which were assembled in two opposing alliances: the Allies (based on the Triple Entente of the United Kingdom, France and Russia) and the Central Powers (originally the Triple Alliance of Germany, Austria-Hungary and Italy). These alliances were both re-organized and expanded as more nations entered the war: Italy, Japan and the United States joined the Allies, and the Ottoman Empire and Bulgaria the Central Powers.