上颌全口义齿的腭隆突、上颌结节、颧突、切牙乳突区属于无牙颌()
全口义齿基托边缘与唇颊沟、舌沟、上颌后堤区及下颌磨牙后垫处相接触的区域属于()
全口义齿覆盖的牙槽嵴与唇颊沟、舌沟、上颌后堤区及下颌磨牙后垫区之间的区域居于()

A．主承托区

B．副承托区

C．边缘封闭区

D．缓冲区

E．翼缘区

some students are lack of the first class _      _ they take their vacations.[ ]

A. Because of    

B. as    

C. before    

D. and