【单选题】
水手应该知道船上吊杆的安全工作负荷。（）
A、Sailors should know the SWL of cranes on board their ship.
B、Sailors should know the SWL of derricks on board their ship.
C、Officers should know the SWL of derricks on board their ship.
D、Officers should know the SWL of cranes on board their ship.
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