龈上洁治器刀刃应与牙面保持在什么角度可提高洁治的效率()
A．角度越小越好
B．65度左右
C．80度左右
D．最好90度
E．大于90度
参考答案：C
—I really thought I would be offered the chance.
—Oh, well, , Jack.
A．you’re right
B．best wishes
C．better luck next time
D．congratulations
什么叫做已收未刷卡？这种现象在上行还是下行较常见？
