Which statement is true while creating subplans using Resource Manager？（）

• A、 The subplan must belong to the consumer group， SYS_GROUP.
• B、 The total CPU usage at any given level must be less than 100%.
• C、 The subplans can be used to restrict the degree of parallelism for a user.
• D、 You can use a resource plan instead of a consumer group to implement a priority ranking within the plan.