1. SALT - Talks to discuss cuts in the nuclear arms race.
The SALT treaties (SALT I & SALT II) were talks between the U.S.S.R & the U.S. on decreasing the amount of intercontinental nuclear missiles that each nation can own, however, it did not limit the amount for any other missile (those with shorter range).
2. Solidarity - The first free trade union in a Communist nation.
I am not very sure about this trade union, but using process of elimination, this would be the answer.
3. Detente - French for "loosening".
Detente is "loosening", usually describing relationships and releasing strain on the relationship.
4. Perestroika - Russian for "restructuring".
Perestroika is used to describe the restructuring of the former USSR nations, as well as the governmental body of Russia as a whole.
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