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问题 单项选择题

当关系引用了属性名以后，关系具有的性质中不包括______。

A)有重复的元组
B)元组上下无序
C)按属性名引用时属性左右无序
D)所有属性值都是原子项

答案

参考答案：A

解析： 当关系引用了属性名以后具有以下性质：不能有重复的元组，元组上下无序，按属性名引用时属性左右无序，所有属性值都是原子项(不可再分)。

改错题

假如英语课上老师要求同桌之间交换修改作文，请你修改你同桌的以下作文。文中共有10处语言错误，每句中最多有两处。每处错误仅涉及一个单词的增加，删除或修改。

增加：在缺少单词处加一个漏字符合(︿)，并在其下面写出该加的词。

删除：把多余的词用斜线(\)划掉。

修改：在错的词下划 横线，并在该下面写出修改后的词。

注意：1.每处错误及其修改均仅限一词；

2.只允许修改10处，多者（从第11处起）不计分。

Last Saturday, I wanted very much to see a film together with my brother after supper. On my way to the cinema, we happen to meet an American named Peter, who had lost his way, looked worried. When he told us that he wasn't able to find the hotel, we decided take him there. When we went to the hotel, we told of Peter the great changes that had taken place in our country in the past few year, and he told us a lot of things about the youths in the U.S.A.

　 Although my brother and I missed a interesting film, we felt very happily, for we had not only helped Peter out of trouble and also learnt something by him.
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单项选择题 A3型题

患者，女，39岁，6个月前因外伤一上前牙脱落，今要求烤瓷桥修复。口腔检查：右上中切牙缺失，间隙无明显异常，牙槽嵴高度无明显异常，较平整。左上中切牙近中切角缺损，未露髓，探稍敏感，叩诊阴性，无松动。右上侧切牙牙冠完好，叩诊阴性，无松动。上、下前牙牙龈轻度红肿，易出血，可见少量菌斑及牙石，余牙未见明显异常。

下列哪项关于右上侧切牙金瓷冠牙体预备的要求是正确的（）

A.切端磨除2mm

B.唇面磨除2mm

C.牙体预备分次磨除

D.唇面龈边缘在龈沟底

E.唇面龈边缘在龈上
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