Answer:
The Soviet Union had its origins in the Russian Revolution of 1917. Radical leftist revolutionaries overthrew Russia's Czar Nicholas II, ending centuries of Romanov rule. The Bolsheviks established a socialist state in the territory that was once the Russian Empire. A long and bloody civil war followed.
Explanation:
Even though you didn't give us the fragment with the comma slice, it isn't really necessary here as we can answer just based on these 4 options here. All options apart from the second one are correct - only the second option doesn't fix the mistake of the comma splice, whereas the other options do but connecting the sentences properly.
Choose the verbs in the sentence. There are only three of them in this
sentence. Only one of the verbs has a modifier that describes the verb.
That word is your adverb.
