A propeller, in order to operate efficiently, must rotate at a relatively （） speed.

单项选择题Why a gearbox is needed in a ship driven by a medium-speed diesel engine?（）

A.To reduce the main engine speed
B.To increase the main engine speed
C.To govern the main engine speed
D.To fix the propeller shaft

单项选择题Which one is not true?（）

A.Two main areas of skill are involved in the construction of ship
B.There are distinct divisions in responsibilities between naval architects and marine engineers
C.Each ship will assume varying proportions according to its type
D.Ships can be divided into different categories from different perspectives

单项选择题The displacement of a ship is to the total weight, all told, of the relevant loaded ship（）

A.larger
B.equal
C.smaller
D.equivalent

单项选择题When a ship in loaded condition floats at arbitrary water line, its displacement is to the relevant mass of water displaced by the ship（）

A.equal
B.larger
C.smaller
D.equivalent

单项选择题Propulsion engines and the vast majority of auxiliary generator engines are designed to allow a generous through-flow of scavenge air in order to control （）

A.the lubricating oil consumption
B.the turbine blade temperature
C.the flow rate of fuel
D.scavenge air pressure