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Two database users， Jack and Bill， are accessing the Certkiller STAFF table of the Certkiller DB database. When Jack modifies a value in the table， the new value is invisible to Bill.  Which is the modified value invisible to Bill？（）
A:The modified data are not available on disk.
B:The modified data have been flushed out from memory.
C:The modified rows of the Certkiller STAFF table have been locked.
D:Jack has not committed the changes after modifying the value.
E:Both users are accessing the database from two different machines.

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出自：Oracle认证

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