单项选择题
A.possible
B.necessary
C.practicable
D.impracticable
单项选择题 A(n) () is a mechanical attack on the metal surface which may be due to a disturbance in the flow of the water over the blade of the propeller.
单项选择题 A (n) () is a chemical or electro-chemical attack on the metal surface which may be further increased if the sea-water is polluted.
单项选择题 A propeller of 5~65m in diameter, having a mean pitch of 4~88m, turning at 72 rpm, at a speed of 11 knots (339~79m/min), will give () of apparent slip.