栓塞最常见的风湿性心瓣膜病是（）
A.二尖瓣关闭不全
B.主动脉瓣关闭不全
C.二尖瓣狭窄
D.主动脉瓣狭窄
E.三尖瓣狭窄
参考答案：C
— By the way, is Jane in?
— No, she _____ to the school library. [ ]
A. goes
B. went
C. has been
D. has gone
已知二叉树BT的后序遍历序列是dabec，中序遍历序列是debac，它的前序遍历序列是______。
A．cedba
B．acbed
C．decab
D．deabc
