(A) Militarism, Alliances, Imperialism, Favoritism
(B) Majority Rules, Absenteeism, Injuries, Neighbors
(C) ** Militarism, Alliances, Imperialism, Nationalism
(D) Mechanism, Alliances, Injuries, Nationalism
EXPLANATIONS BELOW
Concept note-1: -The war started mainly because of four aspects: Militarism, Alliances, Imperialism and Nationalism. This is because big armies become potential threats to other countries, other countries started forcing alliances in order to secure land.
Concept note-2: -One alliance included Germany, Austria-Hungary and Italy, called the Triple Alliance. Opposing them was the Triple Entente of France, Russia and England. These complex tensions finally exploded into war.