(A) Bolsheviks
(B) Armistice
(C) ** Trench warfare
(D) Unrestricted submarine warfare.
EXPLANATIONS BELOW
Concept note-1: -Trench Warfare kept World War I at a stalemate for the first few years of fighting. Trench warfare was used for most of the war on the western front . Long lines of trenches were dug by both sides to protect the soldiers from gunfire and artillery.
Concept note-2: -During World War I, trench warfare was a defensive military tactic used extensively by both sides, allowing soldiers some protection from enemy fire but also hindering troops from readily advancing and thus prolonging the war. Trench warfare was the major combat tactic in France and Belgium.
Concept note-3: -Trench life involved long periods of boredom mixed with brief periods of terror. The threat of death kept soldiers constantly on edge, while poor living conditions and a lack of sleep wore away at their health and stamina.
Concept note-4: -The Western Front of World War I is infamous for trench warfare, long and grueling battles fought from dug-in positions separated by no man’s land.
Concept note-5: -Trench warfare in World War I was employed primarily on the Western Front, an area of northern France and Belgium that saw combat between German troops and Allied forces from France, Great Britain and, later, the United States.