Little Tommy was reluctant to tell the schoolmaster__________he had done the day before.

A．that

B．how

C．what

D．where

中空义齿是指（）

A.下颌骨缺损的始导板

B.上颌骨缺损部的阻塞器义齿

C.唇腭裂序列治疗的语音训练器

D.腭、咽部损部的阻塞器

E.颜面部缺损赝复体