问题：
[单选题]有一个关系：学生（学号，姓名，系别），规定学号的值域是8个数字组成的字符串，这一规则属于
A、实体完整性约束
B、参照完整性约束
C、用户自定义完整性约束
D、关键字完整性约束
参考答案：
C
相关内容
- ● 在应用ORS液的过程中，错误的作法是（）
- ● 一项关于吸烟与肺癌关系的病例对照研究，研究结果表明OR为4.0，其意义是（）
- ● 在应用ORS液的过程中，错误的是（）
- ● Mainly eat 3 or 4 partly cloudy to overcat occaional rain（）lowly outh moderate or good.
- ● （）any cae or upected cae of quarantinable dieae，or any cae of eruptive dieae or any death be dicovered，the local quarantine officer mut be notified immediately．
- ● Should any cae or upected cae of quarantinable dieae，or any cae of eruptive dieae or any death be dicovered，the local Quarantine Officer mut be（）immediately.
- ● Mater are（）olely reponible for all damage or accident of whatever kind reulting from the navigating or handling of their veel by day or by night.
- ● If he i a common carrier，he i abolutely reponible to the owner of the good carried （）any lo or damage to them unle caued by an Act of God or the Queen’ enemie，or the inherent vice in the good themelve，or the negligence of the owner of the good，or a general average acrifice.
- ● 系统中雷达状态包括Unknown、Operational（or ON）、Failed（or OFF）、Detached。
- ● Owner are to be reponible for lo of or damage to the good or delay in delivery of the good only in cae the lo，damage or delay ha been caued by the improper or negligent towage of the good．Thi mean that（）.
- ● The carrier i liable for lo of or damage to the good or delay in delivery caued by fire，（）the claimant prove that the fire aroe from fault or neglect on the part of the carrier，hi ervant or agent.
- ● Shutdown price（or point，or rule） 停业价格（或停业点、停业原则）
