第7题: [单项选择]Questions 11-13 are based on the following talk.
Why is the woman waiting A. She is waiting for the man. B. She is waiting for her mother. C. She is waiting for a bus. D. She is waiting for the rain to stop. 参考答案:C 答案解析:[听力原文] 11-13 M: Excuse me. Have you been waiting long W: About ten minutes. M: Did you not
第8题: [单项选择]一个不好的数据库可能出现( )问题。 Ⅰ、数据冗余 Ⅱ、更新异常 Ⅲ、插入异常 Ⅳ、删除异常 A. Ⅱ、Ⅲ、Ⅳ B. Ⅰ C. Ⅰ、Ⅱ、Ⅲ D. Ⅰ、Ⅱ、Ⅲ、Ⅳ 参考答案:D 答案解析:[解析] 一个“不好”的关系数据库模式存在以下问题：
①数据冗余。
②更新异常(不一致的危险)。由于数据冗余，有可能使我们在一个元组中更改了某属性，而没有更改另一个元组中的同一属性，与实际情况
