The correct option is C Forming the Warsaw Pact.
The Warsaw Pact, formally known as the Treaty of Friendship, Cooperation and Mutual Assistance, was a collective defence treaty signed in Warsaw, Poland between the Soviet Union and seven Eastern Bloc satellite states of Central and Eastern Europe in May 1955, during the Cold War. The Warsaw Pact was the military complement to the Council for Mutual Economic Assistance, the regional economic organization for the socialist states of Central and Eastern Europe.