单项选择题
A.for FP, once fitted, the position of the blades can also be changed in operation
B.for CP, once fitted, the position of the blades can also be changed in operation
C.the CP type has a relatively smaller hub compared with the FP propellers
D.the FP type has a relatively larger hub compared with the CP propellers
单项选择题 The propeller consists of a （）with several blades of helicoidal form attached to it.
单项选择题 Oil pressure in the lubrication system is（）than the static sea water head to ensure that sea water cannot enter the sterntube in the event of seal failure.
单项选择题 （）is used to prevent the entry of sea water to the machinery space.