Final answer:
The Triple Alliance consisted of Germany, Austria-Hungary, and initially Italy as a mutual defense agreement among European powers prior to World War I. The correct options are a,b,c.
Step-by-step explanation:
The Triple Alliance prior to World War I was an agreement between three European nations/empires, which included Germany, the Austro-Hungarian Empire, and Italy. This alliance was essentially a mutual defense agreement in which each member pledged to come to the defense of the others in case they were attacked by another great power, notably France or Russia.
Despite being a signatory to the Triple Alliance, Italy did not enter World War I on the side of the Central Powers; instead, it joined the Allies in 1915. Throughout the war, the Central Powers were mainly comprised of Germany, Austria-Hungary, and the Ottoman Empire, with the latter joining after the war had begun.