9.使用下列何種裝置於植體覆蓋式義齒不具應力緩衝(stress-breaking)之效果?(A)單一磁性(magnetic)支柱牙(B)蛋型道爾得槓(egg-shaped Dolder bar)(C)球狀附連體(ball attachments)(D)套疊式鑄造牙冠(cast telescopic copings)