完形填空。阅读下面短文，从自短文后所给的四个选项（A、B、C和D）中选出能填入空白处的最佳选项。（每小题1.5分，满分30分）
It had been a tiring day and I was looking forward to__31__ evening. My husband__32__ back until late and I had __33___ to sit down in a comfortable armchair in the living room and read a book. I __34__ the children to bed early and __35__ a cold supper and some coffee. Soon I was sitting comfortably with a plate __36___ with food before me and a book at my side.
I was just beginning to eat __37__ the telephone rang. I put down my knife and fork and hurried to answer __38___ . By the time I got back to the living room，my coffee __39__ cold. After I finished my __40__ I began to drink my coffee __41__ my book open at page one. Suddenly there was a __42__ at the door. It gave me __43__ surprise that I spilt the __44__ and made an ugly stain（污迹）on my skirt. Some stranger had got __45__ and wanted me to show him the way. It __46__ ages to get rid of him. At last I __47__ to sit down again __48__ actually read a whole page without __49__ more interruption until the baby woke up. He began crying loudly and I rushed up-stairs. The baby was __50__ awake at eleven o'clock when my husband came home. I should have cried myself when he asked me if I had a pleasant evening！
31. A. a quiet B. an exciting C. a lovely D. a lonely
32. A. would come B. had not come C. came D. would not come
33. A. decided B. started C. come D. hurried
34. A. put B. made C. threw D. allowed
35. A. boiled B. heated C. cooked D. prepared
36. A. full B. filled C. filling D. to be filled
37. A. as B. then C. when D. while
38. A. him B. her C. it D. them
39. A. was getting B. had got C. would get D. got
40. A. supper B. drinking C. reading D. coffee
41. A. while B. when C. as D. with
42. A. stranger B. loud knock C. dog D. man
43. A. such great B. a so great C. such a great D. so great
44. A. food B. supper C. plate D. coffee
45. A. gone B. lost C. missing D. away
46. A. cost B. spent C. paid D. took
47. A. tried B. hoped C. decided D. managed
48. A. before B. after C. but D. and
49. A. some B. any C. much D. no
50. A. already B. still C. possibly D. almost
木板中点处，物体B与A之间的动摩擦因数为μ=0.1，B与A间的最大静摩擦力等于滑动摩擦力（B可看作质点，重力加速度g取10m/s2）。求：