A disadvantage of using chain lashing on heavy vehicles aboard Ro-Ro vessels is that it is （）.

单项选择题A device fitted over the discharge opening on a relief valve consisting of one or two woven wire fabrics is called a flame（）.

A.stopper
B.screen
C.filter
D.restrictor

单项选择题A decrease in barometric pressure is associated with all of the following except（）.

A.rising warm air
B.proximity to a low pressure area
C.inward spiraling circulation
D.clear dry weather

单项选择题（）during the voyage any case or suspected case of plague，cholera，yellow fever，smallpox，typhus or relapsing fever?

A.Has there been
B.Have there been
C.Has there
D.Have there

单项选择题（）day，pilot flag should be displayed from main mast.

A.From
B.By
C.on
D.With

单项选择题（）any sick person on board now apart from the above-mentioned cases?

A.Have
B.Has
C.Is there
D.Are there