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.