Why did the Allied Powers eventually gain an advantage in th…

Why did the Allied Powers eventually gain an advantage in the war, leading to surrender of the Central Powers in 1918? a) The U.S. sending millions of troops actually helped the Germans by motivating them to be more aggressive b) A good summer harvest in the summers of 1917 and 1918 increased the Centrral Powers food supply, and “Food Will Win the War” c) The Russian Revolution hurt the Central Powers d) The Central Powers mounted an all-out attack in France near the Somme, which failed, and all hope was lost