What happened in Russia in 1917 that led the United States to justify its involvement in World War I as a fight for democracy?

ARussia signed a military defense treaty with France and Great Britain.

BRussia signed the Treaty of Brest-Litovsk and made peace with the Germans.

CRussian revolutionaries overthrew the Czar and established a provisional government.

DRussian Bolsheviks, under Vladimir Lenin's leadership, toppled the provisional government.