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（）.
单项选择题 （）during the voyage any case or suspected case of plague，cholera，yellow fever，smallpox，typhus or relapsing fever?
单项选择题 （）day，pilot flag should be displayed from main mast.
