圆锥形套筒冠中，固位支持型固位体内冠内聚角为
A．6°B．2°～5°C．8°D．10°E．45°
参考答案：A
--Are you a teacher?
--No, but I ________.
A．used to
B．was used to
C．used to be
D．used to do
