减压塔的塔径发生变化，但塔板间距不发生变化。
参考答案：错
— I can't recite the poem.
— Well, you are supposed _____ it many times yesterday evening. [ ]
A. to read
B. reading
C. to have read
D. having read
分解因式：x2﹣y2﹣2y﹣1=( )
