第5题: [单项选择]What is the woman’s job A. Sympathetic. B. Unconcerned. C. Amused. D. Hopeful. 参考答案:A 答案解析:[听力原文] W: Have you heard about Harry M: No. What happened W: He was fired last week. M
第9题: [单项选择]设U是所有属性的集合,X、Y、Z都是U的子集,且Z=U—X—Y。下面关于多值依赖 的叙述中,______是不正确的。 A. 若X→→Y,则X→→Z B. 若X→Y,则X→→Y C. 若X→→Y,且Y’ Y,则X→→Y’ D. 若Z=Ф,则X→→Y 参考答案:C 答案解析:若X→→Y在R(U)上成立,且Y’ Y,不能断言X→→Y’在R(U)上成立。这是因为多值依赖的定义中 涉及了U中除X,Y之外的其余属性Z,考虑X→→Y’是否成立时涉及的其余属性Z’=U—X—Y’比确定
第25题: [单项选择]A. Its texture. B. Its size. C. Its preservation. D. Its shape. 参考答案:B 答案解析:[听力原文] What aspect of the hidden biosphere does the man discuss