You have created a resource plan, DB_PLAN, using DBMS_RESOURCE_MANAGER.CREATE_SIMPLE_PLAN and you want to impose a restriction on utilization of resources by the database users.  <br /> Which step must be performed before you can start using the resource plan?()
A、assign users to consumer groups
B、set the resource plan for the instance
C、configure a simple resource plan and specify plan directives
D、configure a complex resource plan and specify plan directives