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[单选题]
如果某个属性不包含在候选键中,则它称为()
A
非主属性b.关键属性c.复合属性d.主属性
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参考答案
试题答案:
A
答案解释:
该题考查对主属性和非主属性的理解。包含在任何一个候选键中的属性称为主属性;不包含在任何一个候选键中的属性称为非主属性。所以A项是正确选项。
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第31答案是( ) 查看材料
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23. I was walking along the deserted main street of a small seaside town in the north of England looking for somewhere to make a phone call. My car had broken down outside the town and I wanted to contact the AA. The street ran parallel to the sea and was joined to it by a number of narrow side streets. Low grey clouds were drifting across the sky and there was a cold damp wind blowing off the sea which nearly threw me off my feet every time I crossed one of the side streets. It has rained in the night and water was dripping from the bare trees that lined the street. I was glad that I was wearing a thick coat.There was no sight of a call box, nor was there anyone at that early hour whom I could ask. I had thought I might find a shop open selling the Sunday papers or a milkman doing his rounds, but the town was completely dead. The only living creature I saw was a thin frightened cat which was hopelessly sniffing at some empty paper bags that had been dropped outside the fish-and-chip(炸鱼与马铃薯片) shop the night before.Then suddenly I found what I was looking for. There was a small post office, and almost hidden from sight in a dark alley next to it was the town's only public call box, which badly needed a coat of paint. I hurried forward, but stopped in astonishment when I saw through the dirty glass that it was already occupied. There was a man inside. He was very fat, and was wearing a cheap blue plastic raincoat and rubber boots. I could not see his face- he was bending forward over the phone with his enormous back pressed against the glass and did not even raise his head at the sound of my approaching footsteps.Discreetly(小心地), I remained standing a few feet away and lit a cigarette to wait my turn. It was when I threw the dead match on the ground that I noticed something bright red flowing in drops from under the call box door.(10分)23.1 According to the passage, the A(Para. 1) is most probably____.(2分)A. a hotel providing accommodations for traveling motoristB. the local police stationC. a British motoring organization that helps members when their cars break downD. an inquiry office
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