单项选择题
A supercharged engine differs from an un-supercharged engine it operates at an increases pressure（）.
A.in which B.on which C.at which D.in that
单项选择题 Cooling makes the engine metals their mechanical properties（）.
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 （）.
