Following the Bolshevik Revolution, Lenin a. put a socialist system in place
b. entered World War I on the side of the Central Powers
c. held free, open, and democratic elections
d. restored the Romanov monarchy

a.

Explanation:

answer; ///i believe that the correct answer is (a) the great depression

although world war i began in 1914, the united states did not join the war until 1917. the additional firepower, resources, and soldiers of the u.s. to tip the balance of the war in favor of the allies. remaining neutral. when war broke out in 1914, the united states had a policy of neutrality.