He is rather difficult to make friends with, but his friendship, _____ is more true than anyone else’s.

A．Once gaining

B．Once gained

C．Once is gaining

D．Once he gained

根据考古，（）是已知的商代时期医学文字记录的载体。

A.竹简

B.石头

C.甲骨

D.帛

E.纸张