（2x+3）（______）=9-4x2
（3-2x）（3+2x）=9-4x2．
所填结果是：-2x+3．
Gina was _____ in 1999. She is old enough to go to school.[ ]
A. bear
B. bore
C. born
D. bears
对如下二叉树： ABDECF 进行后序遍历的结果为______。
A．ABCDEF
B．DBEAFC
C．ABDECF
D．DEBFCA
