The United States is wellknown 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 centers 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. Although B. Since C. Because D. Therefore
37. A. rough B. splendid C. smooth D. complicated
38. A. little B. few C. much D. many
39. A. selections B. separations C. divisions D. sections
40. A. terrible B. Possible C. enjoyable D. reasonable
41. A. to B. Into C. over D. by
42. A. lead B. connect C. collect D. provide
43. A. large B. fast C. light D. heavy
44. A. when B. for C. but D. that
45. A. yet B. still C. almost D. quite
46. A. unless B. if C. as D. since
47. A. relatively B. regularly C. reasonably D. respectively
48. A. and B. Less C. more D. or
49. A. All B. Several C. Lots D. Some
50. A. driving B. crossing C. curving D. traveling
51. A. rocks B. cliffs C. roads D. paths
52. A. lying B. laying C. laid D. lied
53. A. there B. when C. which D. where
54. A. space B. period C. chance D. spot
55. A. view B. variety C. visit D. Virtue
，则在此过程中质点所受合外力的大小 （选填“变大”、“变小”或“不变”），质点与水平面之间的动摩擦因数等于_________。
可得，当其运动一周时，速度减小，所以向心力减小，故合外力减小，过程中摩擦力做负功，根据动能定理可得
，解得