You execute the following block of code：   SQL>BEGIN   DBMS_RESOURCE_MANAGER.CREATE_SIMPLE_PLAN   （ SIMPLE_PLAN => ’DEPARTMENTS’，   CONSUMER_GROUP1 => ’PAYROLLL’，   GROUP1_CPU => 50，   CONSUMER_GROUP2 => ’SALES’，   GROUP2_CPU => 25，   CONSUMER_GROUP3 => ’MARKETING’，   GROUP3_CPU => 25）；   END；   SQL>/   What is a prerequisite for using the simple resource plan created by executing the above code？（）

• A、 You must assign users to consumer groups.
• B、 You must grant the switch privilege to the users.
• C、 You must create a resource plan directive.
• D、 You must specify the complex resource plan.