A. As an officer on duty, you must know how to adjust derricks.
B. As a sailor on duty, you must know how to adjust derricks.
C. As a sailor on duty, you must know how to operate cranes.
D. As an officer on duty, you must know how to operate cranes.

A. Many ships have two derricks at each hatch.
B. Many ships have two winches at each hatch.
C. Many ships have two derricks and two winches at each hatch.
D. Many ships have two derricks and two winches at each hatch cover.