(A) The collapse of the Russian front
(B) ** The entry of the U.S. into the war
(C) The invasion of Normandy
EXPLANATIONS BELOW
Concept note-1: -Stalemate describes a condition in war in which neither side can change the front lines dramatically no matter how hard it tries. WWII never reached stalemate in Europe. The opponents alternated offensive and defensive campaigns but were almost always moving. World War I epitomized stalemate.
Concept note-2: -Stalemate: A situation in which further action is blocked; a deadlock. Stalemate is a commonly known term in the game of chess. In it, all the pieces – pawns, rooks, bishops, knights, kings and queens – are frozen, questioning if there is another move to be made, what direction to go and how to escape defeat.
Concept note-3: -In 1918, a series of major German and Allied offensives broke the stalemate of trench warfare on the Western Front, resulting in the near-collapse of the German Army and the end of the fighting before the end of the year.
Concept note-4: -In 1917, Germany adopted a defensive strategy on the Western Front to counter the growing strength of the Allies. Despite launching several offensives, and suffering heavy casualties, the Allies achieved mixed results.