单项选择题
The propeller is pushed on to the tubeshaft taper and made tight by（）
A.a mechanical seal B.keyway and key C.a nut D.shrinkage
单项选择题 For a propeller direct driven by the engine,（）.
单项选择题 Propeller running at （） are generally efficient.
单项选择题 Which is not the maintenance work for shaft bearings in transmission system?（）
