The war on the western front was a stalemate by 1916. what was the effect of this development?

Neither side was able to make progress in the war and this was the effect of the stalemate of 1916 of the war in the western front. During World War I, the western front was considered as the main theater of war. After the outbreak of the war, the Germans opened up a front in the western part and started progressing until the progress was halted by the Battle of Marne. 

The correct answer is c