Correct answer: mass production. The first mass-production vehicle manufacturing plant (the cheap automobiles) was a result of Henry Ford´s innovations in assembly-line techniques and the introduction of standardized interchangeable parts.
In response to growing demand at that time, a new factory was built and it had everything to construct the vehicles (including a steel mill, glass factory, and the first automobile assembly line). Ford was able to market to the general public.
Henry Ford was also responsible for his factory to function on a three-shift workday and operate 24 hours a day.