49. A. in           B. with           C. by               D. on

48. A. safe         B. slow           C. boring            D. dangerous

47. A. people         B. trains           C. cars              D. planes

46. A. on            B. by              C. with             D. in

45. A. pollution       B. air              C. environment      D. place

44. A. costs          B. takes            C. spends           D. uses

43. A. since          B. unless           C. until             D. so

42. A. as for          B. and also         C. so that           D. not only

41. A. earlier         B. faster           C. later             D. cheaper

40. --I wonder if he          ,me with my English.

   --If I           you, I'd phone him and ask.

     A. will help, are                        B. will help, had been

     C. will help, were                       D. helps, were

     The bike is one of the simplest yet most useful inventions in the world. What is the                                                            

most surprising is that it was not invented 41, although the great inventor Lenardo da Vinci had drawn pictures for bikes 42 for flying machines and some other things. Those things were not produced  43  long after he died.

     A person riding a bike 44  very little energy to make it move, and there is no45  at all when he is riding one. Even so, in developed countries, most people don't go to work  46 bike. It is not because the bikes are expensive. It's because the number of 47 on the road becomes larger. It certainly becomes more   48  to ride a bike. As a result, more people put their bikes away and go to work in their cars, and 49 this way, the situation is made more serious. Perhaps the best way to make bike riding safer and more 50 is to create paths only for bikes, and to make it so difficult and expensive for drivers to ride to in their cars into the city that they will go back to use their bikes.