Which was an effect of the russian revolution on world war 1? a. the united states enter the war b. germany invaded russia on two fronts c. serbian nationalist formed an alliance with the ottomans d. russia surrendered to germany

C. Serbian nationalist formed an alliance with the ottomans 

The others are wrong:

A) is wrong, because: The US joined the war because of the torpedoing of Lusitania, and the Zimmermann telegram, not because of the Russian Revolution
B) is wrong, because: Germany cannot invade in two fronts. Germany invaded only from the west, and that was mostly in WW2.
D) is wrong, because: Russia technically did not 'surrender' to Germany. Instead, they signed a armistice, which stopped fighting between the two.

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