题目

下列方程有实数根的是（） A . x2+10=0 B . x2+x+1=0 C . x2﹣x﹣1=0 D . x2﹣ x+1=0 答案：CThe Unit States is well―known for its network of major highways designed to help a driver get from one place to another in the shortest possible time.  36  these wide modern roads are generally  37  and well maintained, with  38  sharp curves and many straight  39  , a direct route is not always the most  40  one. Large highways often pass  41 scenic areas and interesting small towns. Furthermore, these highways generally  42  large urban center which means that they become crowded with  43  traffic during rush hours,  44  the “fast, direct” way becomes a very slow route. However, there is  45  always another route to take  46  you are not in a hurry. Not far from the  47  new “superhighways”, there are often older,  48  heavily traveled roads which go through the countryside.  49  of these are good two lane roads; others are uneven roads  50  through the country. These secondary routes may go up steep slopes, along hilly  51  or down frightening hillsides to towns  52  in deep valleys. Though these are less direct routes, longer and slower, they generally go to places  53  the air is clear and the scenery is beautiful, and the driver may have a  54  to get a fresh, clean  55  of the world. 36. A. AlthoughB. SinceC. BecauseD. Therefore37. A. roughB. splendidC. smoothD. complicated38. A. littleB. fewC. muchD. many39. A. selectionsB. separationsC. divisionsD. sections40  A. terribleB. possibleC. enjoyableD. reasonable41. A. toB. intoC. overD. by42. A. leadB. connectC. collectD. provide43. A. largeB. fastC. lightD. heavy44. A. whenB. forC. butD. that45. A. yetB. stillC. almostD. quite46. A. unlessB. ifC. asD. since47. A. relativelyB. regularlyC. reasonablyD. respectively48. A. andB. lessC. moreD. or49. A. AllB. SeveralC. LotsD. Some50. A. drivingB. crossingC. curvingD. traveling51. A. rocksB. cliffsC. roadsD. paths52. A. lyingB. layingC. laidD. lied53. A. thereB. whenC. whichD. where54. A. spaceB. periodC. chanceD. spot55. A. viewB. varietyC. visitD. virtue