Which syntax turns an existing constraint on?（）

• A、ALTER TABLE table_name   ENABLE constraint_name;
• B、ALTER TABLE table_name   STATUS = ENABLE CONSTRAINT constraint_name;
• C、ALTER TABLE table_name   ENABLE CONSTRAINT constraint_name;
• D、ALTER TABLE table_name   STATUS ENABLE CONSTRAINT constraint_name;
• E、ALTER TABLE table_name   TURN ON CONSTRAINT constraint_name;