单项选择题
To maintain the down stream pressure within defined limits over a range of flow and despite any changes in supply pressure, （） is fitted.
A.a check valve
B.a gate valve
C.a pressure reducing valve
D.a quick closing valve
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A.at most references
B.at least references
C.maximum standards
D.minimum standards -
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Annex IV of MARPOL 73/78 contains regulations for the prevention of （）.
A.pollution by oil
B.pollution by noxious liquid substances carried in bulk
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The SOLAS Convention in its successive forms is generally regarded as the most important of all international treaties concerning the （） of merchant ships.
A.pollution
B.economization
C.safety
D.efficiency
