磁性材料生产中常用的压力单位有MPa和()两种。
参考答案:kg/cm2
---I wanted to be a soldier when I was a little boy.
--- .
A.So I was
B.So was I
C.So I did
D.So did I
数据库系统由硬件系统、数据库集合、______、数据库管理员和用户所组成。