Imagine a world where air pollution is no longer a problem. Clean air is all around us. People don't have to worry about polluting the air every time they drive their cars. They no longer need to face the problem of not having enough fuel either. Although scientists have been trying for many years to develop a new kind of car that does not need gasoline  , _ have been unsuccessful. Recently, however, car engineers have succeeded in creating a new kind of car that runs on gasoline and electricity . This is the famous "hybrid car". This car gets its name from the fact that it has a gasoline engine   and an electric motor inside. Hybrid cars do not pollute the environment as much as the cars that are commonly used today. They also cost drivers less money because they need less fuel than ordinary cars. Hybrid cars are becoming widely popular in the United States. They are soon expected to become widely used around the world. If scientists and engineers continue to work on car development, perhaps the world with clean air that we imagined earlier just might become real in the future. The passage tells us that with the development of cars, we may   _  .
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