單項(xiàng)選擇題

The EMPLOYEES table has six indexes and DML operations are slow. Which command begins monitoring the EMPLOYEE_IDX_FK index to determine whether it has been used by an execution plan?()

A.ALTER TABLE employees monitor index employee_idx_fk; 
B.ALTER INDEX employee_idx_fk monitoring on; 
C.ALTER TABLE employees monitor all indexes; 
D.ALTER INDEX employee_idx_fk monitoring usage; 

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