The ________look on his face showed that he hadn’t expected it.

A．astonished

B．astonishing

C．being astonished

D．having astonished

正畸施力只有牙槽骨的吸收，却没有或只有少量的牙骨质吸收的原因是（）

A．牙骨质硬

B．牙槽骨修复能力强

C．牙根表面总是覆盖着一薄层尚未钙化的类牙骨质

D．牙周膜内环境的稳定性

E．颌骨可塑性强