有极昼极夜现象的是( )
A:热带
B:北温带
C:南寒带
D:南温带
已知x﹣y=3,则代数式(x+1)2﹣2x+y(y﹣2x)的值是____
-- Tom made mistakes in the exam in our class.
-- So he did. Because he did it .