您要对EMPLOYEES表的FIRST_NAME和LAST_NAME列创建一个组合索引。以下哪条语句将完成此任务()A、CREATE INDEXfl_idx ON employees(first_name last_name)B、CREATE INDEXfl_idx ON employees(first_name),employees(last_name)C、CREATE INDEXfl_idx ON employees(first_name,last_name)D、CREATE INDEXfl_idx