The correct answer is C) The dismantling of the Berlin Wall and the end of restrictions on emigrating from communist countries.
A significant long-term cause of the collapse of the Soviet Union during the late twentieth century was the dismantling of the Berlin Wall and the end of restrictions on emigrating from communist countries.
After many years under the Communist regime, the Soviet Union split in December 1991. During those Communist years, the USSR never allowed private property in the Soviet United. The state was the owner of the means of production.
So when Gorbachev decided to implement glasnost and perestroika reformations, he had to carefully proceed because these involved some kind of risk. Glasnost allowed people more rights such as the freedom of speech and freedom of the press. Perestroika allowed new and private investments to revitalize the difficult economic conditions of Russia.
The Soviet Union ceased to exist on December 26, 1991. Gorbachev had resigned one day before and the new leader of Russia was Boris Yeltsin.