What is the passage mainly aboutt

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 31 to 35.

When the automobile was first invented, few people thought of buying one. Gradually, as cars were improved, more people wanted to buy them. Designers tried to think of improved ways to manufacture automobiles. Finally, Henry Ford set up a factory with an assembly line to produce automobiles. Even with this 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, the United States. Then the cars were shipped to wholesalers all over the country. Wholesalers bought the cars from the factory and sold them to auto dealers in each city. The dealers 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 dealer, the wholesaler’s job was unnecessary. The dealers 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 one 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.

What is the passage mainly about?

• A. . automobile manufacturing in the United States
• B. industries that have changed
• C. the job of a wholesaler
• D. how to sell cars in Detroit, Michigan