Answer:
A. Russia adopted a communist government, but Western European
countries did not.
Step-by-step explanation:
In Western Europe, the war was largely a stalemate as a result of extensive trench warfare that gave the defenders a massive advantage during battles. In Russia, however, the monarchy was overthrown by rebels, who then negotiated peace and surrendered large chunks of land to the Germans, allowing them to concentrate all their troops and resources to the Western Front.