SDH帧结构中，B字节的用途是（）。

A．再生段追踪

B．误码检测

C．使用者通路

D．公务联络

Deadweight, which is the cargo carrying capacity of a vessel in tons, is determined by（）.

A.loaded displacement minus light displacement

B.gross tonnage minus net tonnage

C.loaded displacement minus net tonnage

D.light displacement minus the weight of the vessel