The USSR leader who implemented the policy of "Perestroika" to restructure and reform their economy and political systems was Mikhail Gorbachev.
Explanation:
1. Mikhail Gorbachev served as the General Secretary of the Communist Party of the Soviet Union from 1985 to 1991.
2. Perestroika, meaning "restructuring" in Russian, was a significant reform introduced by Gorbachev to modernize the Soviet economy and political system.
3. Under Perestroika, Gorbachev aimed to decentralize the Soviet economy by allowing more autonomy to enterprises, promoting market mechanisms, and encouraging openness and transparency in governance.
4. The policy of Perestroika was part of Gorbachev's broader reform agenda, which also included Glasnost (meaning "openness") to increase political openness and freedom of speech in the Soviet Union.
5. The implementation of Perestroika played a crucial role in the eventual dissolution of the Soviet Union and the end of the Cold War.
Therefore, the correct answer to the question is:
d) Mikhail Gorbachev
