牙体粘结修复术洞形制备的特点是（）。

A.前牙切角缺损不必磨除正常釉质

B.不承受颌力处，可形成盒状洞形

C.可不做预防性扩展

D.洞缘的釉质壁不必做短斜面

E.垫底时可过多覆盖牙本质

Peter ________ under the pressure of his position and was unable to work for a year.[ ]

A．settled down  

B．broke down

C．passed away  

D．broke out