The areas that were part of the USSR from the options provided are:
Belarus, Crimea, and Ukraine.
- Belarus was a founding republic of the USSR.
- Ukraine was also a founding republic of the USSR.
- Crimea was part of the Russian Soviet Federative Socialist Republic and later transferred to Ukraine during the Soviet era.
Finland and Poland were never part of the USSR. Siberia is a region within Russia, which was the largest constituent republic of the USSR, but is more of a geographic region than a separate entity that can be classified similarly to Belarus or Ukraine.
Therefore, the correct answer from the options given is Ukraine, Belarus, and Crimea.