单项选择题
A.An air compressor B.An indicator cock C.An air distributor D.A safety valve
（） may have two emergency source of power, thus requiri...
单项选择题（） may have two emergency source of power, thus requiring two emergency switchboards.
A.Large passenger vessels B.General cargo ships C.Container ships D.Oil tankers
（） usually helps to induce air movement to assist combu...
单项选择题（） usually helps to induce air movement to assist combustion.
A.Cylinder cover B.Main bearing C.The exhaust valve D.The piston movement
（） is secured by means of side-chock bolts and end-choc...
单项选择题（） is secured by means of side-chock bolts and end-chock bolts.
A.The bedplate B.The column C.The main bearing D.The double bottom
