A、There was not enough room to make the Detroit factory bigger. B、There were no enough workers in Detroit. C、It was no longer pr

When the automobile was first invented, few people thought of buying one. Gradually, as cars were improved, more people wanted to buy them. Men tried to think of new and better ways to manufacture automobiles. Finally, Henry Ford set up a factory with an assembly line to produce automobiles.
    Even with his new system of manufacturing the automobile industry remained fairly small. Almost all the assembly work was done in a few large factories near Detroit, Michigan. Then the cars were shipped to wholesalers all over the country. Wholesalers bought the cars from the factory and sold them to auto traders in each city. The traders then sold the cars to the people who wanted to buy them.
    During the 1920s, this system began to change. The automobile industry had grown rapidly. Soon it was no longer practical to have assembly plants in Detroit only. New plants were built all over the country. With plants near each trader, the wholesaler’ s job was unnecessary. The traders could buy cars directly from the factory.
    Many other kinds of industries have moved their factories from the cities to small towns. In place of large factory, these companies now have several smaller plants. Like the automobile industry, they have found that many small factories can be more efficient than fewer large plants.