用循环水冷却的冷换设备在引循环水时应注意的是：在冷换设备进出口管线的高点处打开放空阀将管道和冷换设备内的空气排净。
参考答案：对
________we went to visit Professor Smith, he________his research work.
A．The first time; devoted to
B．Whenever; was concentrate on
C．For the first time; was busy with
D．Each time; was absorbed in
用链接方式存储的队列，在进行删除运算时，下面操作正确的是( )。
A．仅修改头指针
B．仅修改尾指针
C．头、尾指针都要修改
D．头、尾指针可能都要修改
