单项选择题 The （） engine is used for alternators and some times for main propulsion with a gearbox to provide a propeller of between 90 to 120 rpm.

单项选择题 The （） of the main shaft should be measured with a （）.

单项选择题 Such an engine frame helps （） the engine and so protect the bearings from the deformation forces transmitted via the ships double bottom.