单项选择题
Which of the following is not correct? （）
A.It is useless to complain. B.It is useless complaining. C.Complaining is useless. D.It is useless of complaining.
单项选择题 He seemed to be unaware（）the trouble he was causing.
单项选择题 I can't see（）between these two books
单项选择题 Letters, maps and pictures are（）
