A、To make it at a low cost. B、To make it easy for everyone to fix. C、To make it not easily be broken down. D、To make it availabl

　　(19) When cars first started appearing on the street in the world, there were only few people who took them seriously, because they thought they were toys—play things for grown men who didn’t have much time to play. No one thought that the automobile would ever become the world’s most popular form of transportation after many years. When Henry Ford started selling his Model T in 1908, he changed the situation. Ford believed that a car should be the low-cost transportation that everyone could afford, so he decided to make such a car. First he wanted a dependable automobile that wouldn’t break down easily. Then he wanted a simple engine that almost anyone could repair. (20) Ford wanted to sell the car at a low price so that many people who were not very rich could afford one. And because of this, he had to make it at a very low cost. Finally, he made only one model in only one color—black. In 1932, the Duesenberg brothers produced a car that many people thought as the brightest automobile ever made. The very car called Duesenberg was custom-made, so each one was different. But it usually weighed about 7 000 pounds and had a very wide wheelbase which was 150 inches. It also had an enormous 400 horsepower engine that could move the car from 0 to 100 miles per hour in 17 seconds.
　　19.  How did people think of cars when they first started appearing on the street?
　　20.  Why did Henry Ford make only one model in only one color?
　　21.  What does the passage mainly talk about?