21.  The ringing would be heard by others.

22.  So he covered his cars with something, thinking that everything would be all right and that he could get the doorbell without any trouble.

23.  The ten week: The next week will be our exam time.

24.  This must be changed by us .

25.  The next week will be our exam time.

26.  I will be very grateful to you for your help.

27.  But his daughter Mary was afraid that the trip would be o much for him.

28.  When I came into class and sat down, my Chinese teacher introduced me to all the pupils who were in my class, then they looked at me, I was so afraid, I thought they must be laughing at me .

29.  Life of people can't be good and also can't be bad all the time.

30.  that time we used to be happy, but then everything was changed .