离心泵动密封摩擦副的材料一般不选()。
A、陶瓷
B、青铜
C、碳钢
D、碳--石墨
参考答案:C
She was working in the room suddenly she heard a boy crying and ____ out as quickly as she could to see what was happening.
A.went
B.going
C.go
D.had gone
一个双面5英寸软盘,每面40道,每道8个扇区,每个扇区512个字节,则盘片总容量为(1)。若该盘驱动器转速为600转/分,则平均等待时间为(2),最大数据传输率为(3)。
空白(2)处应选择()
A.25ms
B.50ms
C.100ms
D.200ms