How did the USSR exert control over Hungary?

The correct choice highlights the methods the USSR used to maintain control over Hungary during the mid-20th century, particularly during and after the 1956 Hungarian Revolution. Following the revolution, which aimed to establish greater independence from Soviet influence, the USSR responded with military intervention and repression. This involved jailing dissenters, executing opponents of the government, and manipulating the political landscape to ensure that pro-Soviet communists remained in power. These actions were part of a broader strategy to crush any form of opposition and ensure that Hungary remained firmly within the Soviet sphere of influence.

The other options do not accurately reflect the historical context. Supporting free elections would be contrary to the Soviet Union's interests, especially given the chaos following the revolution. Executing economic policies, while part of the control, does not encapsulate the aggressive methods of political repression employed. Establishing capitalist systems directly contradicts the fundamental tenets of Soviet ideology, which was based on a communist model of governance and economy. Thus, the methods of jailing or killing opponents and winning elections directly illustrate how the USSR maintained its grip on Hungary.