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You execute the following command in your Certkiller .com production database to change the width of the CUST_NAME column of the CUSTOMERS table： ALTER TABLE customers  MODIFY （cust_nameVARCHAR2 （40）） /  When you execute the command， it displays the following error message：  ERROR at line 1：  ORA-00054： resource busy and acquire with NOWAIT specified  What could be the reason for the error message？（）
A:The database instance is not available.
B:The ALTER TABLE command does not have WAIT option
C:The table or a row in the table is currently locked by another user session.
D:The database instance is busy processing other user sessions commands.
E:The CUSTOMERS table has no long running query active at the time when this request is made.
F:The server process executing the ALTER TABLE command is busy with another command execution

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出自：Oracle认证

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