熟化石灰粉可采用磨细生石灰，亦可用（）代替。
A.生石灰
B.石粉
C.电石粉
D.粉煤灰
参考答案：D
---Why does the lake smell terrible?
---Because large quantities of water________.[ ]
A.have polluted
B.is being polluted
C.has been polluted
D.have been polluted
已知二叉树后序遍历序列是dabec，中序遍历序列是debac，它的前序遍历序列是( )。
A．acbed
B．decab
C．deabc
D．cedba
