反锁是指（）

A.上后牙的近中颊尖位于下后牙的中央窝，面有咬合接触

B.下后牙的远中颊尖位于上后牙的中央窝，面有咬合接触

C.上后牙的舌斜面位于下后牙颊斜面的颊侧，面无咬合接触

D.上后牙颊尖的颊斜面位于下后牙舌尖舌斜面的舌侧，面无咬合接触

E.上后牙的舌斜面位于下后牙颊斜面的舌侧，面有咬合接触

Tom was absent from school this morning, because sometimes he was a little weak and could ______ill .

A．take

B．set

C．catch

D．fall