The bicycle is one of the simplest yet most useful inventions in the world. What is the most surprising is that it was not1 earlier, although the great inventor Leonardo Da Vinci had drawn pictures for bicycles and2 for flying machines and some other things. Those things were not produced3 long after he died.
A person riding a bicycle uses4 energy(能量)to make the bicycle move, and there is no 5 at all when you are riding. Even so, in developed 6 most people do not travel to work by bicycle. It is not because the bicycles are expensive or people feel7 if they ride to work. It is because 8 cars on the roads is becoming larger. It certainly be-comes9 to ride a bicycle. As a result, more people put their bicycles away and go to work10 their cars. And in this way, the situation is becoming11 .
12 the best way to make riding safer and more popular is 13 paths only for bi-cycles, and to make14 so difficult and expensive for drivers to take their cars into the city.15 they will go back to use their bicycles.
