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The bicycle is one of the simplest but （1）
inventions in the world.What is the most surprising is that it was not （2）
earlier，although the great inventor Leonardo da Vinci had （3）
pictures for bicycles and flying machines and some other things.Those things were not produced （4）
long after he died.
A person riding a bicycle uses very little energy to make the bicycle （5）
，and there is no pollution at all when he is riding.Even so，in most developed （6）
，most people don't go to work by bicycle.It is not because bicycles are expensive or people feel （7）
if they ride to work.It's because the number of cars on the roads becomes larger.It certainly becomes more （8）
to ride a bicycle.As a result，more people put their bicycles away and go to work （9）
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 （10）
roads only for bicycles.
