Which act authorized a thorough study of commercial aviation?

The Air Mail Act of 1934 is the correct choice because it aimed to reorganize and improve the air mail system, which included a comprehensive evaluation of the state of commercial aviation at the time. This act was significant in shaping the future of the aviation industry by addressing various issues related to air mail contracts and the operations of commercial airlines. By establishing regulations that focused on safety and efficiency in air transportation, it effectively laid the groundwork for the expansion and modernization of commercial aviation practices.

The other acts mentioned did contribute to the development of aviation, but they did not specifically authorize a thorough study of commercial aviation in the same way. For instance, the Air Mail Act of 1925 primarily aimed at allowing private companies to carry mail, while the Air Commerce Act of 1926 focused on promoting safety and developing airways. The Federal Aviation Act of 1958 established the FAA and set the stage for federal regulation of commercial aviation, but it came much later and was part of a broader spectrum of evolution in aviation regulations.