第9题: [单项选择]对关系模式进行规范化的目的是( ),并避免出现插入异常、删除异常和更新异常。 A. 减少数据冗余 B. 提高查询速度 C. 保证数据安全 D. 提高查询效率 参考答案:A 答案解析:[解析] 一个“不好”的关系数据库模式会存在数据冗余、更新异常(不一致的危险)、插入异常和删除异常四个问题。为了解决这些问题,人们才提出了关系数据库的规范化理论。规范化理论研究的是关系模式中各属性之间
第30题: [单项选择]{{B}} Questions 11 to 18 are based on the conversation you have just heard.{{/B}} A. The woman goes to school during the day and works at night. B. The woman has to work to support herself. C. The woman’s classes are not difficult. D. The woman studies at night. 参考答案:D 答案解析:[听力原文]
M: How do you manage to work and to go to school at the same time
W: My classes are at nig