The bicycle is one of the __41__ yet most useful inventions in the world. The surprising thing is that it was not __42__ earlier, although the great inventor Leonardo Da Vinci  (达芬奇)  had drawn pictures for bicycles and also for flying machines and some __43__ things. Those things were not produced __44__ long after he died.

A person riding a bicycle uses __45__ energy (能源) to make the bicycle move, and there is no pollution at all when you are riding. Even so, in developed __46__ , most people don't travel or work by bicycle. It's because   __47__ cars on the roads is larger and larger. It certainly becomes __48__ to ride a bicycle. As a result, more people put their bicycles away and go to work __49__ their cars. Perhaps the best way to make riding safer and more popular is to build roads only for __50__, and to make it difficult and expensive for drivers to drive their cars into the city.

41. A. simple         B. simpler            C. simplest           D. more simple

42. A. invent          B. inventing           C. invention           D. invented

43. A. other           B. another            C. others             D. the other

44. A. until           B. when             C. since              D. after

45. A. much           B. no                C. quite a lot of       D. very little

46. A. world          B. countries          C. land               D. villages

47. A. the number of   B. a number of        C. this kind of        D. many kinds of

48. A. safer            B. more dangerous    C. much dangerous    D. more wonderful

49. A. by             B. use               C. in                 D. riding

50. A. buses           B. cars               C. trains              D. bicycles