制作金属烤瓷基底蜡型时，在金瓷交界处应做成（）。

A.凸面

B.凹面

C.锐面

D.直角

E.斜面

The official number of a documented vessel is（）.

A.not required to be anywhere on the vessel

B.required to be permanently marked on the vessel's structure

C.required to be painted on the vessel;s stern

D.required to be painted on the vessel's bow