单项选择题
A.analysis
B.design
C.installation
D.upgrade
单项选择题 The（）schemeinadatabasesystemisresponsibleforthedetectionoffailuresandfortherestorationofthedatabasetoastatethatexistedbeforetheoccurrenceofthefailure.
单项选择题 （）statementcanperformacalculationandstoretheresultinavariablesothatitcanbeusedlater.
单项选择题 Dataitemsareaddedordeletedfromthelistonlyatthetopofthe（）.