The Soviet Union was made of Federated 15 states. Option C is correct.
Of them, Russia was considered the most powerful.
The Soviet Union, in other words, the Union of Soviet Socialist Republics was a socialist state located in Eurasia that existed from 1922 to 1991. The Sobiet Union constituted a union of multiple national Soviet republics, and its government and economy were centralized.
In its final years, the Soviet Union encompassed Soviet Socialist Republics (S.S.R.’s): Armenia, Azerbaijan, Belorussia (now Belarus), Estonia, Georgia, Kazakhstan, Kirgiziya (now Kyrgyzstan), Latvia, Lithuania, Moldavia (now Moldova), Russia, Tajikistan, Turkmenistan, Ukraine, and Uzbekistan. The capital was Moscow, then and now the capital of Russia.