Answer:
D: The machine gun
Explanation:
There were a lot of stalemates across the European nations as although the Allies possessed an edge in almost all areas, the Central powers were not far behind. The machine helped to continue these stalemates as they fired at around 500 RPM. It was hard for infantry troops to mount an attack on a trench or to move back enemies when they were getting mowed down. Attacks by the French to move the German front lines back ended in long lists of casualties.
