为使基牙牙周应力分布均匀，支托凹底与基牙长轴的夹角应为（）
A.10°
B.20°
C.30°
D.40°
E.60°
参考答案：B
My friend Mary is _________beautiful girl, _________girl everyone likes to work with.
A．a , a
B．a , the
C．the, a
D． the , the
X波道中，DME/N的系统延时为（）。
A.12μs
B.50μs
C.60μs
