Having taken our seats, ______.

A．the professor began the lecture

B．the lecture began in no time

C．we were attracted by the lecture immediately

D．the bell announced the beginning of the lecture

圆锥型套筒冠固位体内冠厚度一般是（）

A.0.15mm

B.0.2mm

C.0.3mm

D.0.4mm

E.0.5mm