單項選擇題Foam-type portable fire extinguishers are more usefull in combating fires involving（）.

A.solid materials such as wood or bales of fiber
B.inflammable liquids
C.electrical equipment
D.metallic solids


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1.單項選擇題For a floating vessel, the center of buoyancy and the metacenter are in the line of action of the buoyant force（）.

A.only when there is positive stability
B.only when there is negative stability
C.only when there is neutral stability
D.at all times

2.單項選擇題For a floating vessel,the center of the floating is the point in the waterpiane.（）.

A.aboat which the vessel lists and trims
B.which coincides with the center of buoyancy
C.which, in the absence of external forces, is always vertically aligned with the center of gravity
D.which is shown in the hydrostatic tables as VCB

3.單項選擇題For a floating vessel,the result of subtracting KG from KM is the（）.

A.height of the metacenter
B.height of the righting arm
C.height of the center of buoyancy
D.metacentric height

4.單項選擇題For a floating vessel,true mean draft is always the（）.

A.average of the observed drafts
B.draft at the centre of flotation
C.draft corresponding to the center of buoyancy
D.metacentric height