I suggest the problems worthy to be paid attention to        at the class meeting.

A．discussing

B．discussing

C．be discussed

D．being discussed

以下哪个无牙颌解剖结构属于口腔前庭区内结构

A．腭小凹
B．上颌硬区
C．下颌隆突
D．颧突
E．腭皱