60. It is very important ______ (not give) your goldfish too much food.

59. It took him much time ______(mend) the broken bike yesterday.

58. We will go fishing if it ______ (not rain) tomorrow.

57.I spend half an hour _______(clean) the fish tank every day.

56. The Internet ______(connect) the computer networks all over the world.

55. You ought to _______(use) English more often.

54. Listen, someone _______(knock) at the door.

53. Paul tried ______ (open) the door but failed.

52. A kilo of beef ______ (cost) 10 yuan.

51. Yesterday I ______(lose) my watch.