The "boom" years of the 1920's were characterized by what?

The invention of mass producing the automobile in the 1920's was a part of the "boom." Therefore the widespread use of the automobile and an increase in buying is how the 1920's "boom" years were characterized.

The "boom" years of the 1920's were characterized by a growth in the use of Automobiles.

While looking at the history of the United States, the 'boom years' of the early 1920s were marked by a huge change in the way people traveled.

Personal transportation was shifting from horse-driven carriages to Automobiles, recently mass-produced by Ford.

At the time, the automobiles were a clear sign of growing economic might of the United States and the optimism of the early 1920s.