单项选择题

The first old "horseless carriage" of the 1880s may have been worthy of a snicker or two, but not the cars of today. The progress that has been made over the last one hundred years has been phenomenal. In fact, much progress was made in the first twenty years—in 1903, cars could travel at 70 miles per hour. The major change from the old cars to today is the expense. Whereas cars were once a luxury that only the very wealthy could afford, today, people of all income levels own cars.
In fact, there are so many cars that if they were to line up end to end, they would touch the moon. Cars are used for everyday transportation for millions of people, for recreation, and for work. Many people’s jobs depend on cars—police officers, health care workers, and taxi drivers all rely on automobiles.
One thing that hasn’t changed is how cars are powered. The first cars ran on gas and diesel fuel just as the most modern ones do. The new cars, however, are much more fuel efficient and much research is devoted to saving fuel and finding new sources of energy for cars.

According to the passage, scientists devote much of their research today to（）

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