Although there are no classes in the afternoon now, no student ______ go out of school without the head teacher’s permission.

A．will

B．must

C．may

D．shall

为加强上全口固位需作上颌后堤沟，后堤沟位于

A．前颤动线处

B．后颤动线处

C．软、硬腭之间

D．腭小凹与两侧翼上颌切迹连线后约2mm处

E．腭小凹与上颁结节连线后1mm处