换热器使用和切换时应()
A.开时先通冷流体,后通热流体
B.开时先通热流体,后通冷流体
C.先关闭在用换热器进出口阀门,再启用备用换热器
D.关时先关冷流体,后关热流体
参考答案:A
It ____________ twelve hours to go to Guangzhou by train.[ ]
A. is taking
B. are going to take
C. takes
D. has taken
为什么公司原则上不得成为自己的股东?