牙槽骨水平吸收时形成的牙周袋通常为（）

A.骨上袋

B.骨内袋

C.复杂袋

D.一壁骨袋

E.四壁骨袋

Ordinary people are now lacking of the scientific knowledge about nutrition.

A. short with


B. are absent of
C. lack in



D. are deficient on