Tom wants to be a professor when he _________.[ ]

A. grow up  

B. growing up  

C. grows up  

D. grew up

Sharpey纤维是指（）。

A.一端埋在牙槽骨，一端埋入牙龈

B.一端埋在牙槽骨，一端埋入牙骨质

C.一端埋在牙槽骨，一端埋入牙周膜

D.一端埋入牙骨质，一端埋入牙周膜

E.一端埋入牙髓，一端埋入牙龈