The bicycle is one of the simplest but most useful invention

The bicycle is one of the simplest but most useful inventions in the world.What is most surprising is that it was not _36___early,although the great inventor Leonardo da Vinci had drawn pictures for bicycles and also for flying machines and some other things.Those things were not produced_37___long after he died.
A person riding a bike uses __38__energy（能源） to make the bicycle move ,and there is no pollution at all when you are riding.Even so,in developed _39__,most people don’t travel to work by bicycle.It is not because the bicycles are dear or people feel __40__if they ride to work.It’s because_41___cars on the roads becomes larger.It certainly becomes_42__to ride a bike.As a result,more people put their bikes away and go to work__43__their cars and ,in this way,the situation is made more serious.__44__the best way to make riding safer and more popular is to create paths (开设通道) only for bicycles and to make__45__so difficult and expensive for drivers to take cars into the city that they will go back to use their bicycles.
36 .A.invent B.inventing C.invented
37.A.before B.until C.when
38.A.very little B.quite a lot of C.much
39.A.world B.countries C.land
40.A.lucky.B.glad C.tired
41.A.the number of B.a number of C.this kind of
42.A.safer B.more dangerous C.much dangerous
43.A.by B.in C.use
44.A.Hardly B.May be C.Perhaps
45.A.it B.them C.that