The correct answer is D) Russia
The Russian Empire, ruled by the Romanov dynasty, was focused in the problems of the WWI when the majority of the Russian population, that lived in very poor conditions, started a revolutionary movement led by Vladimir Lenin and the Communist party. This movement overthrew the imperial government in October 1917 and established the first Communist government known as the Union of Soviet Socialist Republics. One of the first measures the new government took was to withdraw from the war since it was seen as a war where workers from different countries went to die for Bourgeois interests.