Final answer:
The Allies needed the help of American soldiers in 1917 and 1918, with German submarines sinking one in three Allied ships. The arrival of over a million US troops following a failed German offensive in 1918 was critical in pushing back German forces and shifting the momentum in favor of the Allies.The correct option is b).
Step-by-step explanation:
The Allies desperately needed the help of American soldiers during 1917 and 1918, when years of trench warfare had exhausted their resources and morale. After a failed offensive in spring of 1918, some of the French troops refused to continue fighting. The situation was dire as German submarines, or U-boats, were wreaking havoc on Allied shipping, sinking one in three ships that left British ports. The introduction of the American naval escorts and the convoy system improved the situation, but the physical presence of the American army was the turning point in the war.
In the face of shipping losses, widespread food shortages, and the impact of the British blockade on Germany's war effort, the German command recognized that their only hope was a desperate offensive in 1918. However, after initial successes, they failed to sustain their victories. The arrival of over a million US troops began pushing German forces back and was a fatal blow to German hopes of dominating the Western Front and led to a significant momentum shift in favor of the Allies.