Cars are lots of fun, but they could also be dangerous. We have to be careful when we drive them or ride in them. It’s always a good idea to put on your seat belt when you’re in a car. Why? Think about this example: Y ou put an egg on a skateboard ( 滑板) and give it a push. If the skateboard hits a stone, it will stop, but the egg won’t . I t will fly through the air, hit the ground and break. Now think what would happen if you tied the egg to the skateboard. W hen the skateboard hits a stone, the egg won ’ t go flying. It will stay safely on the skateboard . Volvo, a famous Swedish carmaker, was the first to use seat belts in 1949. Air bags are also very important for car safety, seat belts could even hurt the people who wear them. Most newer cars have air bags in front of and next to the seats. When a car hits something, its airbags will come out quickly — in less than one second — to keep the people inside safe.