The correct answer is - cooperation in the development of space technology.
The Apollo-Soyuz Test Project, was a true testament that the two biggest world powers can collaborate and be productive together, as well as be able to put their differences aside because of common interest.
Prior to the Apollo-Soyuz Test Project, the United States and the Soviet Union, instead of collaborating, they were racing between each other as to who is the better one, and they were on the edge of making a new world war at any time because of the tensions between them. Fortunately, that didn't happened, and they managed to find a common language for the best of all.
