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b) During the 1920s and 1930s great progress was made in the field of aviation, including the first transatlantic flight of Alcock and Brown in 1919, Charles Lindbergh's solo transatlantic flight in 1927, and Charles Kingsford Smith's transpacific flight the following year.

d) One of the most successful designs of this period was the Douglas DC-3, which became the first airliner to be profitable carrying passengers exclusively, starting the modern era of passenger airline service.

c) By the beginning of World War II, many towns and cities had built airports, and there were numerous qualified pilots available.

a) The war brought many innovations to aviation, including the first jet aircraft and the first liquid-fueled rockets.