题目内容

给定关系模式R(U,F),U={A,B,C,D,E,F},F={B→F,D→A,A→E, AE→B},那么属性A的闭包为(62),R的候选关键字为(63)。

ADE
B. ABE
C. ABCE
D. ABEF

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A.The terrible noise in the library.B.The heat inside the library.C.The small room in

A. The terrible noise in the library.
B. The heat inside the library.
C. The small room in the library.
D. The air conditioner of poor quality.

A.Prof. Brown has got into trouble.B.The woman regrets taking up much of Prof. Brown's

A. Prof. Brown has got into trouble.
B. The woman regrets taking up much of Prof. Brown's time.
C. Prof. Brown has difficulty in sleeping.
D. The woman knows Prof. Brown has been busy.

NASA and the Associated Landscape Contractors of America(ALCA) have【B5】the findings of a 2-year study that【B6】the common indoor plant may provide a natural way of helping【B7】"Sick Building Syndrome."
Research【B8】the use of biological processes as a means of solving environmental problems, both on the【B9】and in space habitats(栖息地), has been【B10】out for many years by Dr. Bill Wolverton,【B11】a senior research scientist at NASA's John C. Stennis Space Center, Bay St. Louis, Miss.
Based on preliminary evaluations of the use of common indoor plants for indoor air purification and revitalization(恢复活力), ALCA【B12】NASA to fund a study using about a dozen popular varieties of ornamental plants to determine their【B13】in removing several key pollutants associated with indoor air pollution. NASA research on indoor plants has found that living plants are so【B14】at absorbing contaminants in the air that some will be launched into【B15】as part of the biological life support system aboard future orbiting space stations. 【B16】more research is needed, Wolverton says the study has shown that common indoor landscaping plants can remove【B17】pollutants from the indoor environment. "We feel that future results will provide an even【B18】argument that common indoor landscaping plants can be a very effective part of a system used to provide pollution【B19】homes and work places," he【B20】.
【B1】

A. offices
B. plants
C. ways
D. homes

【B18】

A. stronger
B. larger
C. smaller
D. weaker

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