从剖面观察，牙可以分为 （）

A.牙冠、牙髓、牙本质、牙骨质

B.釉质、牙本质、牙骨质、牙髓

C.牙根、牙髓、牙本质、牙骨质

D.牙根、牙颈、牙髓

E.釉质.牙根、牙颈

A diamond or ruby is a jewelry that is often used to decorate valuable ornaments or other special objects such as rings or necklaces.