龈上洁治器刀刃应与牙面保持在什么角度可提高洁治的效率（）。

A.角度越小越好

B.65度左右

C.80度左右

D.最好90度

E.大于90度

Selina _______ the story _______ her sister had left off.

A．picked up ；in which

B．took up ； where

C．ended up ；in which

D．packed up ； where