Why should people call Greyhound for tickets in advance？
A. To avoid waiting in lines at the booking office．
B. To hand in necessary travelling documents．
C. To get tickets from the nearest terminal．
D. To fix the travelling destination in time．
听力原文：Will you be free this weekend？
(5)
A. I'm not in the office.
B. No, I am.
C. I have homework to do.
D. I'm a student.
Night-shift workers are those who ______．
A. have to pay on their internal clock
B. need to re-adjust their clock
C. fall asleep late at night
D. have to work at night
设氮的一次节流液化系统的操作温度为290K和71.9K。假设氮气被等温可逆压缩到10.1MPa，其低压对应于液氮在71.9K的饱和蒸气压(0.05MPa)。如果换热器是理想的，系统没有漏热，该液化器的热力完善度是()。
A. 0.064
B. 0.068
C. 0.087
D. 0.092
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