数据库以文件系统的根本区别在于数据的结构化。
参考答案：错
The young man made a ________ to his parents that he would try to earn his own living after graduation.[ ]
A. prediction
B. promise
C. plan
D. contribution
水泥的代号为P·S。
A．硅酸盐
B．普通硅酸盐
C．矿渣硅酸盐
D．火山灰质硅酸盐
