单项选择题
On a ship，a door that is required to be marked KEEP CLOSED is designed to（）.
A.prevent the passage of flammable gases B.prevent the passage of poisonous vapors C.delay the spread of heat and flames D.maintain watertight integrity
单项选择题 Limit switches are used on which davits?（）
单项选择题 In the piping systems of a vessel，what type of valve gives the least resistance to fluid flow when fully open?（）.
单项选择题 In ship operations，hoisting and lowering pipe in and out of the drilled hole is the main function of the（）.
