Science seems to be getting closer to answering a very old mystery. Homing pigeons can be 　36　 hundreds of miles from their homes. When they are let to go to 　37　 again, they find their way home. Because of this special ability to 　38　,pigeons have been used 　 39　 messengers for hundreds of years.

Today people even breed homing pigeons for 　40　 at a sport. The birds are shipped to some chosen 　41　 a few hundred miles away. Then all of them are let to go together. The winner is the bird that gets home 　42　.A good race can make it home from 500 miles away 　43　 a single day.

　 The mystery of the homing pigeons is how they 　 44　 directions and how they find home. The first part seems to be pretty well 　 45　,and we know of two ways that pigeons tell directions. First, they use the sun. Experiments show that homing pigeons can tell 　46　 by the sun. What happens when the 　47　 is darkly overcoat by clouds and no one can 　48　 where the sun is? Then the pigeons still find their way home.

　Naturally, people have wondered whether pigeons might have a built-in compass　 49　 that would tell them about the direction of the 　　 50 　 magnetic(磁的)field. Many different kinds of experiments were 　 51　 　.Here’s what the scientists decided 　 52　 they had made experiments many times. When pigeons can see the sun, they use it as their 　 　53　 　 means of direction-finding. When they can’t see the sun, they use some 　54　 way to sense direction from the earth’s magnetic field.

　 But how do pigeons know 　55　 direction is toward home? What do they use that we would call a map? These are other questions to be answered.

36. A. carried B. taken　　　　 　　　　　　 C. shipped　　　　 　　　　 D. brought

37. A. escape B. get　　　　　 　　　 C. fly　　　　　　　　　　　　　　　　 D. run

38. A. find home B. sense directions　 C. send messages　　　 D. make friends

39. A.by B. as　　　　　　　　　　 C. for　　　　　 　　　　　　　　　　 D. to

40.A.performing B. directing　　　　　 C. showing　　　 　　　　 D. racing

41.A.place B. port　　　　　　　　 C. city　　　　　　　　　　　　 D. country

42.A.fast B. quickly　　　　　　 C. safely　　　　 　　　　　　　　　 D. first

43.A.on B. at　　　　　　　　　　 C. in　　　　　　 　　　　　　　 D. over

44.A.tell B. recognize　　　　　　　　 C. realize　　　 　　　　　　 D. know

45.A.explained B. answered　　 　　 C. shown　　　　　　　　　　 D. understood

46.A.courses B. roads　　　　　　　 C. directions　　 　　　　　 D. ways

47.A.sun B. heaven　　　　　　　　　　 C. land　　　　　　　　　　　　　　　 D. sky

48.A.see B. find　　　　　　　　　 C. notice　　　　　　　　　　　　　　 D. observe

49.A.anything B. something　 　　 C. someone　　　　　　　　 D. anyone

50.A.earth’s B. sun’s　　　　　　　　 C. planet’s　　　　　　　　　　　　　 D. destination’s

51.A.carried B. done　　　　　　　　 C. taken　　　　　　　　　　　　　　 D. had

52.A.before B. when　　　　　　　　　　　 C. while　　　　　　　　　　　　　　 D. after

53.A.important B. major　　　　　　　 C. main　　　　　　　　　　　　　　　 D. most

54.A.quick B. strange　　　　　　 C. special　　　　　　　　　　　　　 D.easy

55.A.what B. where　　　　　　　　　　 C. how　　　　　　　　　　　　　　　 D. which