The correct answer is C. 1917.
Explanation
The revolutions of February and October 1917 were revolutions of the population of the Russian Empire, against the monarchy headed by Tsar Nicolas II. The February revolution occured from the 8th to the 12th of this month because the population and the opposition to the Tsar disagreed with Russia's participation in the First World War and the poverty that this had caused. As a result of this revolution, the Tsar had to renounce his power, also, a transitional government was implemented. Subsequently, the October revolution occured from 6th to 8th of this month and meant the seizure of power by the socialist party and the creation of Soviet Russia. So, the correct answer is C. 1917.
