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【单选题】
数据库系统由外模式、模式和内模式三级模式构成。下列关于数据库系统三级模式的叙述,正确的是 。A.
模式描述的是数据局部逻辑结构
B.
外模式描述的是数据的全局逻辑结构
C.
内模式描述的是数据物理结构和存储方式
D.
外模式/模式、模式/内模式的映像分别实现了数据的物理独立性和逻辑独立性
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举一反三
【单选题】______ of danger in the street last night, she had to go home, with a friend following her.
A.
To be warned
B.
Warned
C.
Having warned
D.
Warning
【简答题】19-1反光镜式卡曼涡流空气流量计是根据什么理论，利用光电信号通过检测漩涡的频率来测量空气流量的？
【单选题】She w al k alone in the street at night. [来源:Z*xx*k.Com]
A.
did not dare to
B.
not dare
C.
dared not to
D.
are not daring
【简答题】反光镜式卡曼涡流空气流量计是根据什么理论,利用光电信号通过检测漩涡的频率来测量空气流量的?
【单选题】She decided to combine her new idea __________ she gained watching the black dancing in the street with the original one. [ ]
A.
what
B.
where
C.
from which
D.
which
【简答题】Today is Tom’s birthday. After school he walks past the shop on the street corner. He looks at the window. That pair of trainers is still there. He really wants to have them very much. He was very sad...
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