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.
A.reaches to B.gets C.calls on D.calls at
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.
单项选择题 The exhaust valve is opened at about the same time （） the air inlet ports are opened.
