Which three statements are true about SQL plan directives?（）

• A、They are tied to a specific statement or SQL id.
• B、They instruct the maintenance job to collect missing statistics or perform dynamic sampling to generate a more optimal plan.
• C、They are used to gather only missing statistics.
• D、They are created for a query expression where statistics are missing or the cardinality estimates by the optimizer are incorrect.
• E、They instruct the optimizer to create only column group statistics.
• F、Improve plan accuracy by persisting both compilation and execution statistics in the SYSAUX tablespace.