59 下圖中白色問號所指的為牙周韌帶的那一種構造?(A)赫威氏上皮根鞘(Hertwig’s epithelial root sheath)(B)馬拉塞氏殘留體(epithelial cell rests of Malassez)(C)牙骨質結石(cementicle)(D)無細胞無纖維牙骨質(acellular afibrillar cementum)