 Complete the following phrase:  During the existence of the Soviet Union, five objects on the territory of this country were included in the UNESCO World Heritage List. On October 12, 1988, the Union of Soviet Socialist Republics ratified the Convention for the Protection of the World Cultural and Natural Heritage. The first objects located on the territory of the USSR were listed in December 1990 at the . Then five names of objects located in various cities and settlements of the USSR were added to the list. In subsequent years, it was planned to expand this list with other objects on the territory of a huge country, but after exactly a year, in December 1991, the Soviet Union 