第24题: [单项选择]What does the woman mean A. The record player is still useful. B. The man shouldn’t have thrown it away. C. The man should abandon his bad habit. D. She is going to use the record player. 参考答案:C 答案解析:[听力原文] M: I am surprised to see you using the record player I was going to throw away ! W: It
第31题: [单项选择]关系R和S如下表所示,关系代数表达式Π1,4(R∞(下标)R.C<S.B S)的结果为 (201) ,与该表达式等价的SQL语句为 (202) 。 R关系 S关系A.SELECTA,B FROM R,SWHERE C<B B.SELECT R.A,S.B From R,S WHERE R.C<S.B C.SELECT A,B FROM RWHERE C<(SELECTB FROM S) D.SELECT 1,5 FROM RWHERE C<(SELECTB FROM S) 参考答案:B 答案解析:[解析] 关系代数表达式Π1,4(R∞R.C<S.BS)能够选出在R关系的C属性小于S关系的B属,性的连接条件下,属性R.A和S.B。连接条件是R.C<S.B,观察关系R第一行C