M型超声的二尖瓣水平波群不能观察哪项M型曲线（）
A.室间隔
B.左室后壁
C.主动脉瓣
D.右室前壁
E.二尖瓣前壁
参考答案：C
We used to see each other , but I haven’t head from him since last year.
A． especially
B． regularly
C． particularly
D． approximately
栽植胸径7～10厘米落叶乔木坑径×坑深为（）。
A.60cm×50cm
B.70cm×50cm
C.80cm×60cm
D.100cm×70cm
