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.

A.clearance；calipers
B.sinking；bridge gauge
C.diameter；bridge gauge
D.clearance；lead wire

A.to stiffen
B.to soften
C.to loosen
D.to wear

A.prepare to stop the engine
B.assemble an engine on its bedplate
C.make an engine ready for starting
D.make an engine run steadily