How did russia maintain political control?

See below:

Explanation:

During the times, Russia has maintained poltical control by purging party members who are not alligned with their ideaology's and by keeping other political parties away from the main ones by denying them the right to participate, therefore, holding a dominant monopoly in the political party/control center.

Russia

Government and society

During the Soviet era the Russian Soviet Federated Socialist Republic (the R.S.F.S.R.) was subject to a series of Soviet constitutions (1918, 1924, 1936, 1977), under which it nominally was a sovereign socialist state within (after 1936) a federal structure. Until the late 1980s, however, the government was dominated at all levels by the Communist Party of the Soviet Union, which was all-powerful and whose head was the country’s de facto leader. Indeed, in the elections that were held, there was only a single slate of candidates, the great majority of whom were in effect chosen by the Communist Party.

i would say b. or c.