(A) The use of submarines
(B) The soldiers in no-mans land
(C) ** When soldiers fire on one another from opposing lines of dugout trenches.
(D) When soldiers fight at night using machine guns
EXPLANATIONS BELOW
Concept note-1: -What is trench warfare? Trench warfare is a type of combat in which the opposing sides attack, counterattack, and defend from relatively permanent systems of trenches dug into the ground.
Concept note-2: -World War I was a war of trenches. After the early war of movement in the late summer of 1914, artillery and machine guns forced the armies on the Western Front to dig trenches to protect themselves.
Concept note-3: -Trench warfare is the type of land warfare using occupied lines largely comprising military trenches, in which troops are well-protected from the enemy’s small arms fire and are substantially sheltered from artillery.
Concept note-4: -"No Man’s Land” was a popular term during the First World War to describe the area between opposing armies and trench lines.