We should ________ ‘Thank you’ when we borrow something from someone.

A．tell

B．speak

C．say

D．Talk

铸造嵌体片切面的龈缘应伸展到（）

A.自洁区

B.龈外展隙

C.龈缘以上

D.龈沟以内

E.与龈沟平齐