Answer: A, It was fighting a revolution against the tsar and a civil war.
Explanation: It left the war because the war between the white army (Russians) and the Bolsheviks had been fighting. The Bolsheviks wanted Russia to be a communist state, while the Russians were trying to stop the Bolsheviks. The Bolsheviks were led by Vladimir Lenin, wanting to lead the opposition against the Tsar of Russia. Vladimir Lenin would be the first communist leader of Russia.