Hello!
Cotton became the dominant crop after 1793, due to the invention and introduction of the cotton gin by Eli Whitney, which made mass production of cotton possible.
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Answer: Radio broadcasting helped filmmakers discover better ways to capture sound and sync it with moving images.
Since the 20´s and 30´s, when radio broadcasting started becoming mainstream, there were a lot of improvements regarding sound recording equipment, in the form of better quality microphones. That, mixed with the fact that filmmakers started editing sound and post-synchronizing it (instead of recording the sound at the same time that the filming was taking place), has led to a quality increase in the film industry.