The bicycle is one of the simplest and most useful inventions in the world. What is most surprising is that it was not  (发明) earlier, although the great inventor Leonardo da Vinci had drawn pictures of bicycles and also of flying machines and some other things. Those things were not produced until long after he  (死).

    A person riding a bicycle uses a little energy to make the bicycle  (移动), and there is no  (污染) at all when you are riding. Even so, in  (发达的) countries, most people don' t travel to work by bicycle. It is not because the bicycles are expensive or people feel  (疲劳的) if they ride to work. It's because the number of cars on the roads becomes  (更大的). It certainly becomes more  (危险的) to ride a bicycle.

    As a result, more people put their bikes away and go to work in their cars, and in this way, the situation is made more serious. Perhaps the best way to make riding safer and more popular is to  (创造) paths only for bicycles, and to make it so difficult and expensive for (驾驶员) to take their cars into the city that they will go back to using their bicycles.