The bicycle is one of the simplest yet most useful inventions in the world. What is most surprising is that it was not ___(1)___ earlier, although the great inventor Leonardo da Vinci had drawn picture for bicycle and also for flying machines and some other things. Those things were not produced ___(2)___ long after he died. A person riding a bicycle use ___(3)___ energy to make the bicycle move, and there is no pollution at all when you are riding. Even so in developed ___(4)___, most people don't travel to work by bicycle. It is not because the bicycles are expensive or people feel ___(5)___ if they ride to work. It's because ___(6)___ cars on the roads becomes larger. It certainly becomes ___(7)____ to ride a bicycle. As a result, more people put their bicycles away and go to work ___(8)___ their cars, and in this way, the situation is made more serious. ___(9)___ the best way to make riding safer and more popular is to create paths only for bicycle and to make ___(10)___ so difficult and expensive for drivers to take their cars into the city that they will go back to use their bicycles.