Final answer:
During the 1980s, Soviet leader Mikhail Gorbachev introduced perestroika and glasnost as part of his reform efforts. The statement that best completes the diagram is D: Soviet citizens are encouraged to criticize the government.
Step-by-step explanation:
During the 1980s, Soviet leader Mikhail Gorbachev implemented perestroika, which was a policy of restructuring the Soviet economy.
This involved introducing market-like reforms and cutting military spending.
As part of this reform effort, Gorbachev also promoted glasnost, which allowed people to criticize the government and increased openness in politics.
Therefore, the statement that best completes the diagram is D: Soviet citizens are encouraged to criticize the government.