第8题: [单项选择]在教师表中,如果找出职称为“教授”的教师,所采用的关系运算是 A. 选择 B. 投影 C. 连接 D. 自然连接 参考答案:A 答案解析:[解析] 本题考查的是关系运算。选择:从关系中找出满足给定条件的元组的操作。投影:从关系模式中指定若干属性组成新的关系。连接:将两个关系模式拼接成一个更宽的关系模式,生成的新关系中包含满足连接条件的元
第19题: [单项选择]Questions 11 to 18 are based on the conversation you have just heard.A) She wanted to show people her crafts. C) She has seen the exhibition. B) She’d rather go hack home. D) She’s sorry to have missed the exhibit. 参考答案:D 答案解析:[听力原文] M: The native American craft exhibit closed this afternoon. W: Oh, no. I’ve wanted to s