凝汽式透平复水系统进行真空操作的目的是()。
A、降低透平叶轮的运行阻力
B、回收蒸汽凝水,降低生产成本
C、提高蒸汽做功的效率
D、防止透平背压高而联锁透平
参考答案:A, B, C
— According to my grandma, it's a good idea to eat chicken soup when you have a cold.
— ____, scientists agree with her. [ ]
A. Sooner or later
B. Once in a while
C. To be exact
D. Believe it or not.
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