The space race is generally considered to have ended in 1975 when the United States and the Soviet Union collaborated on the Apollo-Soyuz Test Project, where the two nations' spacecraft docked in space and the astronauts from both countries shook hands. This event symbolized a move from competition to cooperation in space exploration. Thus, the correct response is:
"The space race was over in 1975. In that year, the U.S. and the USSR collaborated on a test flight and shook hands when the mission was completed successfully."