Answer:
A) Russia
Step-by-step explanation:
Russia had entered World War One showing compromise for the Serbians, and engaging in a major conflict turned into devastated consequences for the largest Empire of that time.
When Russia entered the conlict, it had the largest army of all, but the heavy casualities that suffered from the Germans were humiliating. A tremend effect on moral .Previously a Ruso-Japanese war had also costed the Tsars a unpopularity that would be devastating.
By the end of year 1917, the Communists overthrew the old regime in most cities and began to introduce a socialist system that soon would turn the reality and give birth to the USSR.
With a new Soviet goverment in turn, the Treaty of Brest-Litovsk signed on March 3, 1918, Russia finally came to conclude terms and started the inner change since the October revolution.
The transformation of Russia into USSR would then accelerate and pose further geopolitical concerns with Germanys defeat years later.