Which of the following weapons helped continue the stalemate on battlefields during World War I?
A. the tank
B. the submarine
C. the fighter plane
D. the machine gun

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.

on april 6, 1917, the u.s. joined its allies--britain, france, and russia--to fight in world war i. under the command of major general john j. pershing, more than 2 million u.s. soldiers fought on battlefields in france.