单项选择题
A.for the release of air from the cooling water
B.providing expansion room for heated cooling water
C.a place for implementing water and water treatment agent
D.all of the above
单项选择题 According to the principle of four stroke diesel engine, what is the number of its efficient work stroke per revolution?（）
单项选择题 What type of electric motor is most commonly used on board ship?（）
单项选择题 Which of the following statements is not true concerning symptom of a fire in the scavenge air box?（）