—When did you get to know the professor over there?

—It was at the work shop     we did reserch to gether two years ago.

A．that

B．there

C．which

D．where

矫治前必须有记录患者牙情况的模型，称之为（）

A.记存模型

B.石膏模型

C.上颌模型

D.初模型

E.终模型