单项选择题
On what type of pump would you find an impeller?（）
A.Centrifugal B.Gear C.Piston D.Vane
单项选择题 On navigational aids，what does the light characteristic Fl(2+1) mean?（）
单项选择题 On cargo booms，preventers are（）.
单项选择题 Mechanical gearing of deck machinery such as the windlass or boat hoists should（）.
