单项选择题
（）, the following possible causes should be investigated.
A.Should the engine stop without apparent reason B.The engine should stop without apparent reason C.The engine stops without apparent reason D.The engine is stopped without apparent reason
单项选择题 We have planned to remove the piston with the help of assistant engineers during the cargo unloading, while the vessel （）port Shanghai.
单项选择题 （）does it take to change the main engine from ahead to astern?
单项选择题 （）, we continued lifting out the pistons.
