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问题 单项选择题

SQL语言的REVOKE语句实现下列哪一种数据控制功能

A．可靠性控制

B．并发性控制

C．安全性控制

D．完整性控制

答案

参考答案：C

解析：所有授予出去的权限可以用 REVOKE语句收回，保证了数据库管理系统的数据安全。

选择题
已知椭圆mx2+ny2=1与直线x+y=1相交于A、B两点，M为AB的中点，O为坐标原点，若直线OM的斜率为
2
，则
n
m
的值为（　　）
A．
2
2
B．
1
2
C．
2
D．2
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补全对话，情景问答
根据对话内容，选择适当的句子补全对话。
A. Do you like it?
B. I like country nusic more than pop music.
C. They are different.
D. So you like them both.
E. How about jazz music?
Girl: I like pop music. __1__
Boy: No, __2__ It's quieter than pop music.
Girl: Yes, __3__ Pop music is a little more exciting than country music.
Boy: __4__
Girl: It's not bad.
Boy: I think it's as good as country music.
Girl: __5__
Boy: That's right.
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