31.  I know about the Can I help you?

32.  I don't know which one is right.

33.  know this question too and changed it .

34.  I know it mean .

35.  me wouldn't know.

36.  I answer is I didn't know too why?

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

38.  and prepare their lessons .Many people know the time is inportant , but they don't know how to use the time to do some useful thing .

39.  Just then a student whom I did not know passed by.

40.  Just then a student whom I did not know passed by.