Which constraint can be defined only at the column level？ （）
A. UNIQUE
B. NOT NULL
CHECK
D. PRIMARY KEY
E. FOREIGN KEY
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WhichofthefollowingcanbeusedinconjunctionwithaFlashbackVersionsQuerytofiltertheresults？（）
ArangeofSCNvalues
B. AlistofSCNvalues
C. Astartingandendingtimestamp
D. Minimumandmaximumsequencevalues
E. Alistofsequencevalues
WhichthreestatementsaretrueregardingthelogicalstructureoftheOracledatabase？（）
A. Eachsegmentcontainsoneormoreextents.
B. Multipletablespacescansharesingledatafile.
C. AdatablockisthesmallestunitofI/Ofordatafiles.
D. Itispossibletohavetablespacesofdifferentblocksizesinadatabase.
EachdatablockinthedatabasealwayscorrespondstooneOSblock.
Yourdatabaseisupandrunningandoneofyourthreecontrolfilesisaccidentallyerased.YoustartRMANandrunthefollowingcommand：RESTORECONTROLFILEFROMAUTOBACKUP；Whichofthefollowingstatementsistrue？（）
A. Thecommandrestoresonlythemissingcontrolfile.
B. Thecommandrestoresallthecontrolfiles.
C. Thecommandfailsbecausethedatabaseisrunning.
D. Thisisthecorrectwaytoaddressthisproblem.
E. Thisisnotthecorrectwaytoaddressthisproblem.
下列观点中，违反唯物辩证法用联系的观点看问题的现象是（）
A. 普高生以后要考大学，所以，他们必须好好学习
B. 对职高生来说，只要学好专业技能课就行了，文化课学不学对以后就业影响不大
C. 职高生不重视文化课的学习，会影响对专业技能知识的掌握和运用
D. 职高生毕业后面临的就业压力并不小于普高生的高考压力，也应该好好学习
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