58. The i_____ population may be the greatest challenge of the world today.

57. The lonely people often r _____ the pets as their family members.

56. We can get more i______ on the Internet.

55. E______ is the best teacher.

54. This story is very interesting. It's w______ reading.

53. Did you n______ the chemical teacher do the experiment?

52. The boy was h ______ by the doctor yesterday.

51.-Is India a d______ country?　 -Yes, I think so.

50. Make sure you have put all the r______ into the dustbin.

49. Can you tell any d______ between the twins ?