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.

50. Sorry, I forgot ______ (do) my homework.

49. He enjoys ______ (play) football instead of ______ (swim).

48. I can’t wait _______(hear) from you.