单项选择题

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