单项选择题
Static electricity may be built up by the（）.
A.flow of petroleum through pipes B.spraying or splashing of petroleum C.settling of solids or water in petroleum D.All of the above
单项选择题 Permission is kindly requested（）the ballast water.
单项选择题 On a ship，a door that is required to be marked KEEP CLOSED is designed to（）.
单项选择题 Limit switches are used on which davits?（）
