将E-R图向关系模型转换时，若将3个实体之间的多对多联系m:n:p转换为关系模式，则该关系模式的关键字为______。
A．任意两个实体的关键字的组合
B．各实体的关键字的组合
C．任意一个实体的任意一个属性
D．任意一个实体的关键字
参考答案：B
解析：[要点解析] 将E-R图转换向关系模型时，3个或3个以上实体之间的一个多元联系可以转换成一个独立的关系模式，与该联系相连的各实体的码以及联系本身的属性均转换为关系的值，而关系的码为各实体码的组合。
The following table shows some results of a survey （调查）in which 800 Japanese school pupils were asked to give their impressions（印象）of their classroom teachers. The pupils’ impressions were found to differ depending on whether the teacher was new (with less than three years’ experience), middle-standing(ten to twenty years), or veteran（有经验的）（twenty to thirty years）. The numbers in the table show the percentage of the pupils who answered “very satisfied” or “extremely satisfied” for each question item （项目）
1. The pupils’ evaluation（评价）can be said to rise at a steady rate（比率）as their teachers’ experience increases in Question Items______. A. I and 4 B. 3 and 5 C. 6 and 8 D. 9 and 10 2. In contrast（对比）to the new teachers, the middle-standing and veteran teachers seem to have made a remarkable（显著的）improvement in their ability to _______. A. be fair to any pupil B. evaluate pupils’ progress C. present materials clearly D. understand and play with pupils 3. Pupils seem to regard the new and the middle-standing teachers as being more_____. A.relaxed in class than the veterans B.interested in pupils’ ideas than the veterans C.neat in appearance than the veterans D.skilful at explaining than the veterans 4. Which of the following statements is true according to the table? A.In the new teachers’ classes, pupils seem to ask questions more freely. B.Pupils seem to be quite satisfied with the amount（量）of time their teachers spend with them between classes. C.The evaluation of the middle-standing teachers is lower than that of the veterans in seven items. D.Though veterans do not play games with pupils during breaks, their teaching is rated highly. |