At What Point Did Russian Participation in the Great War

At what point did Russian participation in the Great War end?

A) when Russia was defeated on the battlefield at the hands of the Germans because Russian industrialization was unable to keep up with German industrialization
B) after Vladimir Lenin had taken power in Russia and was willing to accept harsh terms ending Russian participation in order to concentrate on the ongoing civil war there
C) when Russia threatened to withdraw from the League of Nations because the stipulations of the league would have hurt its economy
D) during the negotiations of the Treaty of Versailles because Vladimir Lenin was affronted when the Allies only offered him negative terms and refused to accept them
E) when Joseph Stalin withdrew all Russian forces from Germany, anticipating that the Allies would soon win the war without Russian intervention