循环氢压缩机的密封油系统的密封油主要有（）等作用。
A、密封作用
B、润滑密封室内的浮环
C、带走热量
D、冷却轴承
参考答案：A, B
________ a lot of trees in this area, but now we can see a tall building instead.
A．There used to have
B．There used to be
C．There is used to having
D．There is used to being
已知一只一般压力表的准确度等级为1.5级，量程10兆帕，求该表的允许基本误差。
