Question

in the 1950s and 1960s, the ussr controlled eastern european nations via a number of methods, including establishing puppet governments and using force to crush any dissent or opposition to communist rule. establishing a blockade along the iron curtain and preventing anyone from entering or leaving those countries. preventing those countries from joining the united nations and creating a policy of containment. encouraging opponents to leave those countries and establishing refugee organizations in western europe

Explanation:

During the Cold War, the USSR established puppet governments in Eastern European countries. These governments were loyal to the Soviet Union. When there was dissent or opposition to communist rule (which was the Soviet - backed system), the USSR used force (such as the Soviet intervention in Hungary in 1956 and Czechoslovakia in 1968).
The Iron Curtain was a metaphorical divide. There was no literal blockade along it in the sense described in option 2. The policy of containment was a US policy (not a Soviet method of controlling Eastern Europe as in option 3). Option 4 is incorrect as the USSR did not encourage opponents to leave and set up refugee organizations in Western Europe.

Answer:

establishing puppet governments and using force to crush any dissent or opposition to communist rule.