冷冻水系统为开式系统的缺点（ ）。
A. 冷水与大气接触，循环水中含氧量高，易腐蚀管道；
B. 水泵的扬程除需要克服管路阻力外，还需具有把水提升到某一高度的压头，因此，水泵扬程和能耗较大；
C. 冷水温度波动较小
D. 如果采用自流回水，回水的管径较大，会增加投资
A hotel's general manager always comes to the guests' rooms to congratulate them on their birthdays.
A. 对
B. 错
PR(Public Relations) Officer is in charge of the Front Office.
A. 对
B. 错
We always introduce the elderly to the young and men to women first.
A. 对
B. 错
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