Task: Question Generation
Input (English): Donald Wills Douglas, Sr. built a plant in 1922 at Clover Field (Santa Monica Airport) for the Douglas Aircraft Company. In 1924, four Douglas-built planes took off from Clover Field to attempt the first aerial circumnavigation of the world. Two planes made it back, after having covered 27,553 miles (44,342 km) in 175 days, and were greeted on their return September 23, 1924, by a crowd of 200,000 (generously estimated). The Douglas Company (later McDonnell Douglas) kept facilities in the city until the 1960s.
Output (English): How Many Planes returned from the circumnavigation in 1924?