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问题 单项选择题

在数据库设计中用关系模型来表示实体和实体间的联系，关系模型的结构是

A．层次结构

B．二维表结构

C．网络结构

D．封装结构

答案

参考答案：B

解析：解析：关系是元组的集合，也就是一个二维表。关系模型的结构就是二维表结构。

单项选择题

A company is considering changing its policy concerning daily working hours. Currently, this company requires all employees to arrive at work at 8 a.m. The proposed policy would permit each employee to decide when to arrive—from as early as 6 a.m. to as late as 11 a.m.
The adoption of this policy would be most likely to decrease employees’ productivity if the employees’ job functions required them to

A．work without interruption from other employees.

B．consult at least once a day with employees from other companies.

C．submit their work for a supervisor’s eventual approval.

D．interact frequently with each other throughout the entire workday.

E．(E) undertake projects that take several days to complete.
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填空题

栈的基本运算有3种：入栈、退栈和 【1】 。
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