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问题 单项选择题

有3个关系R、S和T如下：


由关系R和S通过运算得到关系T，则所使用的运算为( )。

答案

参考答案：D

解析： 关系R与S经交运算后所得到的关系由那些既在R内又在S内的有序组所组成，记为R∩S。

解答题

科幻小说《宇宙之神》一书共有（17万）字．______．
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完形填空

从下面的方框中选择适当的句子填空，使对话完整。

A: May I come in?

B:   小题1: Oh, it’s you, Li Ping. Show me your homework first.

A: Sorry, Mr. Wang. I was not at school yesterday.

B:   小题2:  

A: Something was wrong with my left leg.

B: I’m sorry to hear that.  小题3:  

A: Yes, it’s a little better.

B: You’d better finish your homework this evening.  小题4: . It’s bad for your eyes. You can show it to me tomorrow. You must look after yourself and keep healthy.

A: Yes, Mr. Wang. I must finish my homework after school today.    小题5:  
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