单项选择题
Cooling makes the engine metals their mechanical properties（）.
A.Remain B.to remain C.retain D.to retain
单项选择题 Gas turbines differ from steam turbines in that （）.
单项选择题 The reason why more and more of the large merchant vessels are being powered by medium-speed diesel engines is （）.
单项选择题 The diesel engine is similar to the gasoline engine in that （）.
