51.  This action is a instructive.

52.  know this question too and changed it .

53.  This radio isn't a ordinary radio.

54.  This function was very useful .

55.  this s tesk our students.

56.  I hope our classmates know this question too and changed it.

57.  So he lived with this dog every year.

58.  I hope he will realize this good dreams.

59.  I hope in this surrounding.

60.  We took a one-day trip during this vacation.