--Do you think you will give me a hand in time of trouble?

--I’d like to do something for you ______ everything you’ve done for me.

A．in exchange

B．in turn

C．in return for

D．in terms of

如乙烯塔和乙烯制冷组成开式热泵，那么随着乙烯精馏塔压力降低，热泵压缩机的功耗将减小，热泵系统的节能效率增加。